Here I list the reasons behind why some spell tree just fails, while others are top tier. Debuff sucks. Nobody cares about a diggle losing 2 nimbleness. Nobody will waste mana or a turn for minor debuffs. So it's no surprise nobody ever use the debuff for the debuff. If a debuff is used it's for the damage/disable. AOE spells around the character are useless. Nobody wants to get hit multiples times per turn. Nobody will ever get themselves into that kind of position just to cast, unless we are talking about something with 100% stun. This is why noone use blinding flash or sparkly because they are practically just some super weak single target point blank spell. Break on Defense = Not for Melee. You cannot afford taking turns mid battle to recast that thing while getting hit, unless it's so good it can offset getting hit once. Use meat shield is what gets you killed. Only good one out there is radiance aura, but that's to buff mage's sight range. Break on Offense = Damage Penalty. Anyone is gonna take more than a few swings per battle. And casting it mid battle = 1 less swing. So until the buff out weight the lost damage from the swing, it isn't worth casting. See why noone use viking for melee? I am not losing 2 swings of 60 damage for another 6, nor am I willing to add 4 skill points, use mage equips, just to have 6 damage for the first 5 hits. Upkeep without break mechanism = Good. Timer Duration = Good. Upkeep + Time Duration = Still Good. Notice how those last 3 has many the good buffs that people use? Because at least they last a fight. A tree that uses Corpse requires 1 skill that kills. Otherwise they are good for nothing. Damage and position are possibly the only 2 things mages cares about. The problem now is not the damage, but the super cheap teleport. You can kill damage trees, but as long as 1 damage spell remains usable, mages will remain OP.
I agree I will definitely not actively put myself in positions where I'm surrounded (which is why the only 1-range self-AoE ability I respect is the unarmed one that knocks people back, thus it's useful for getting OUT of such situations). I could be mistaken (haven't used in a while) but I recall the first spell in the fleshsmithing tree to be nearly worthless. The extra 10 life is pseudo-life, once you get hit 5 times (thus take some damage) it disappears and you LOSE 10 life, thus it puts you in a false sense of security which puts you at GREATER risk. That's not to mention that this has upkeep and the only thing it does useful is the +2 health regen. I agree about debuffs, AoE debuffs aren't bad but for the most part, enemies are generally just so similar or they come in hordes that it's just a waste of turns/mana to specifically make one enemy weaker when you could be killing them or doing something else. I can't say too much though, I'm still inexperienced with many of the spell-trees (promethean seems pretty swell though! Probably because it's so direct).
All of the skills you've criticized here are actually quite good (especially after recent changes, such as meat shield now having 12 turns). I think once you play more you'll start to understand their utility.
Debuff skills aren't generally worth it (stun, lockdown, mute ... ALL aside) unless they're passive additions to other attacks, but ... Anchored AoE spells are incredibly useful panic buttons for characters who accidentally become surrounded by blinking, teleport glyphs, invisible monster etc. Let's see you throw Tenebrous Rift at melee range or quickly hack your way back into a chokepoint without a mass knock-back skill. With the right position, you can even still hit a good number of enemies from relative safety using some of these. Brittle buffs can be just as powerful as timed buffs for melee characters, if said characters are dodge or counter focused. You can keep them up without hassle between scattered encounters that might not even hit you once, and they can easily be worth recasting when you have a turn of breathing room before the next mob steps up in monster zoos. Attack-limited buffs aren't for everyday use, but for pure melee characters they are vital advance prep for randomly named bosses, where that one extra turn faster you can kill it can save your arse more than a couple of extra armour absorption would. Although a clever (pure) mage should avoid ever being hit in melee, they still need healing and elemental / magic resistances to not be killed by enemy casters, utility skills to not gib themselves on traps etc. And multiple damaging spells are obviously necessary to deal with single targets vs weak hordes with various elemental resistances themselves. And now we all know!
Yeah. The OP is calling Blinding Flash useless, when it comes at the start of a tree clearly designed from the ground up for gishes, Sparkly same. Debuffs are very weak in the vanilla game, though -- but then there also aren't many of them. I don't get the whole 'no one uses Hiking for melee though -- none of the Viking spells break on attack, do they?
Well, debuffs can be useful because there is a point after which any buffs you could get are pointless (when you have 104 block, it's better to put -3 critical on a monster than it is to get +30 block on yourself), even if the effect isn't the greatest some of the time. The rest of it is a matter of play-style, though. Personally I like breakable and brittle buffs because I'm mostly playing rogue characters so I can easily jump out of combat to re-buff myself if need be, and AoE effects centred on my characters are great when I'm playing rogue-warrior hybrid builds (things that have 3~4 warrior skill trees and 4~3 rogue skill trees). But whatever.
The thing, IMO, about AoE stuff like Tenebrous Rift, and AoE damage in general, is that all of it has... to small AoE. If you can learn the range of it (for examply you can do simple counting and have eyes in your head) you can use it to help you melle stuff in addition to killling everything you're not melleing at the moment. Either I'm a superhuman mathemathician, or anyone can really use tenebrous rift to deal with ANY number of monsters all the time (provided enough mana regen, and most mana regen trees are quite a bit too good at what they do). The thing is there is no downside to using AoE. I never, ever use teleports. I can telly from expirience that in a huge majority of cases teleports are dead skill levels as long as you have a powerfull enough AoE spell which you know the radius of, and you can aim it to hit the squares that a monster meleeing you could occupy. And then you just melle it while whatever youre using to AoE is adding humongous dps.
You are just capable of thinking. It's pretty easy to do that if you try to think, but some players, sadly, don't want to bother doing that.
The point about debuffs is largely that, IMHO of course, the GLGods rather overvalue small stat changes in general. Just look at Armor penalties to Nimbleness, the various debuffs from drunkenness, etc. etc. One of their "big bad evil" debuffs from having an extraplanar being corrupting you was -3 to all primary stats. That's...nothing. And since buffs (and thus debuffs) don't scale, there's a pretty large problem with the capstone delimma and buff/debuff numbers. A HUGE problem.
Well, the big thing is that as players, we *undervalue* changes we can't see. I constantly get complaints about one faction gets +3 AB/AC/Saving throws while another gets an aura that applies -3 AB/AC/Saving throws - and gets no complaints, lol.
I think part of what's happened is that the buffs/debuffs have failed to keep pace with the power of items. Few characters care much about gaining/losing 5 when they're dual-wielding late-game Evil Chest weapons. Even if you lost all your , you'd probably still be able to do OK in melee. The way in which the developers have left primary stat (de)buffs so underpowered is more mystifying. There's nothing complex about the maths involved in the baseline primary stats game - you get 63 to start with, +9 every level-up, and character levels can get into the 30s, so we're talking 350+ in primary stats by the end of the game. For (de)buffs to matter late on, they have to be significant in proportion to numbers like this. The bonus stats in Piracy, Burglary and so on also have to be seen from that perspective - you're getting 10 points instead of 9, which is nice but hardly game-changing.
On the other hand, it might have something to do with the % based nature of many secondary debuffs. If you or buff (or debuff) the pirmary stats hard enough to affect one thing, you're affecting stuff which you might not have wanted to affect. Also, the lot of exotic damages are only reduceable by specific monsters having higher defenses against them, which only really affects things on specific thematic floors (like poison being a bit worthless on lvl2 and frost on lvl 7). Which then means if you get an exotic enough weapon, your damage will be really difficult to reduce through debuffs. And if there were debuffs for exotic damages they'd be really niche, while hosing enough to affect exotic damage weapon wielders would completely cripple someone who's not relying on CoE gear or even luck with it.
One obvious answer to shift the balance away from exotic weapons is to give high-level monsters a small amount of exotic resistance across the board, while reducing armour values a bit. Maybe also give the weapon skills better returns to and so on, since primary stats aren't so dependent on finding good items. It's true that each primary stat affects a range of things, but if small changes in primaries have some disproportionate effect, that's a problem with the whole levelling system, not just with (de)buffs. For instance, the effects of on mana costs are quite a sensitive issue for overall game balance.
A small amount of resist all would just mean that the +2 ring and +1 boots you pick up would mean nothing at all, but the +28 Chest of Evil weapon would still matter. More stat scaling could certainly be an option though.
How about reducing the MAX exotic damage they can take, rather than all of that working the way it does now? Like, adding a cap to high lvl-monsters? Make debuffs which lower the cap?
A better solution would be monsters that reflect a portion of exotic damage dealt. 3 cold? np. 28 necro? lololololol crap.