So I'm rank 27 on the leaderboards (Shelledfade), here are my thoughts on balance. (I play perilous exclusively and have done so for the last 200 hours I've played the game).
There's some things that need to be taken into consideration though. There is no healing class, Guard is absolutely worthless in perilous difficulty, barrier is just way too strong, and enemies hit way too hard in perilous. I think one archer shot in perilous is the equivalent to 45 or 50 constitution. So maybe archers/ranged in perilous need a slight damage reduction while melee enemy damage could stay the same.
1. Arcane warrior is only insanely strong because barrier is insanely overpowered so maybe the fix here is to make a barrier on an arcane warrior weaker than other classes, even if a barrier is cast on it by a keeper it should be weaker than normal, maybe its mana regeneration could also be nerfed because its basically unlimited as long as there's 2-3 enemies nearby. There's fast mana regeneration, then there's what the arcane warrior has which is unlimited mana. lol.
Also people saying arcane warrior is balanced because it doesn't kill fast , well... you're wrong. You are flat out dead wrong. I can kill things as fast if not faster than a reaver with my arcane warrior due to my willpower being at 89 (not the only reason). Pull of the abyss + fade cloak + spirit blade will kill things faster than a reaver if we're comparing each class against each other if I was using a reaver with my willpower compared to my arcane warrior, because you don't have to hunt enemies down one by one on an arcane warrior, you just pull them in the center and kill everything nearly instantly with spirit blade and fade cloak, combine that with a 15% cooldown amulet and its gg. I can literally sit there and tank templar commander until its dead. It's why I feel bad every time I see chain lightning arcane warriors. Fade step / fade cloak / spirit blade / pull of abyss / is the best possible combination you can use. Your spirit blade does more damage than chain lighting and you're aoeing with it because of abyss, making chain lighting absolutely obsolete which is why you take fadestep instead so you don't get hit by archers when you drop an abyss on a group of enemies. It also makes the runs incredibly faster using abyss for the entire group with fade step because you can act as a tank by taking agro first.
But what do I know, I've only promoted my arcane warrior 44 times.
2. legionnaire is a boss but you need the best gear to be able to be effective with it. Guard is useless but not that big of a deal for legionnaire. I think the legionnaire is actually a balanced class, although guard definitely needs to be improved in perilous.
3. Katari, only decent with barrier. It's guard needs to be WAY more effective, because right now guard doesn't help it survive whatsoever making a lot of its skills and passives pointless. Maybe giving the katari rampage would be a good decision for it. It's just overall weak and without a decent keeper or ele casting barrier it really isn't worth playing it at all.
4. Reaver is an interesting case. I don't think its frontal armor works at all right now which is why it goes down in like 2 hits in perilous. Rampage and dragon rage is honestly too strong if we're being serious about balance, because you're basically 100% more effective than an assassin at that point and can't die, making the assassin obsolete as a class. If they fixed its armor and the old rampage bug properly and you have a 15% cooldown reduction amulet, a heal on kill ring, decent cunning from promotes and use sulevin blade or axe of the dragon hunter I can see it being stronger than arcane warrior. The problem is if you take away the ability to use rampage with dragon rage, its basically the same thing as a katari that can heal from normal swings. Yes you can use rampage and do normal swings but that just makes classes uniqueness as a berzerker pointless. I think the reavers armor should be fixed, and I think you should be able to use rampage with dragon rage. I think the real problem is that dragon rage + rampage does WAY too much damage and it heals the reaver too much. Make the class effective, but only once they get decent gear.
5. Elementalist is pretty balanced, only problem I can see is that firestorm is too strong. Firestorm meteors need to be CHANCE of knockdown, not a 100% knockdown if a meteor hits an enemy. That's the only balance recommendation I would make here. Maybe 40% chance of knockdown from meteor would make it more balanced.
6. Keeper is balanced as a support class, although using a improved static cage ring makes static cage last longer than intended. Once they fix that problem with static cage, I wouldn't change anything about it.
7. Assassin is balanced when you get good gear in my opinion, the problem here is that enemy A.I is broken regarding a lot of things and it needs to be improved.If an assassin goes stealth it should break all current agro from enemy a.i however it does not. If they are being targeted by a despair demons ice beam and they stealth they still get targeted by it. The same thing happens from any ranged attack with the current a.i, if an enemy a.i is currently in the animation of casting any type of ranged attack and you stealth, it won't break their targeting, they will still go for you until the attack is finished. There's also some issues of enemies somehow being able to spot the assassin and swinging at them when they shouldn't be able to. The last thing about the assassin is that its kind of annoying to play it in perilous because it only becomes truly effective as a combat class at around level 15-16. Shadowstrike has problems as well. It's hit range is way too short and it doesn't reduce cooldown of stealth when you kill something with it. I don't even think the damage bonus from being in stealth and using shadowstirke actually works. Also I've killed things with the assassins normal attacks and twin fangs and sometimes it doesn't reset the cooldown of stealth, some kind of lag bug I'm guessing.
I'd rework its skill tree a bit so it can be a bit more viable at levels 10-12 in perilous, otherwise it feels like you're being carried/playing as dead weight until around 15-16 unfortunately. I have two red birth blades and two 20% flank damage bonus rings for my assassin and its honestly one of my favorite classes to play but the skill tree is designed to only make it very effective at a higher level and unfortunately there are big problems with stealth and the a.i like I explained, as well as stealth cooldown bugs due to lag. Other than changing where some skills are placed within the skill tree I wouldn't change anything about the class itself though. Just improve stealth/a.i and fix shadowstrike.
8. Necromancer is good. Blizzard however, is not. It's a useless waste of a skill. I wouldn't nerf anything about the class but I would increase the damage of blizzard or make it actually freeze enemies faster so that blizzard is not a completely useless skill. Spirit mark is also useless, and the summon it makes is equally as useless. If anything blizzard and spirit mark need major buffs.
9. Archer is good. Wouldn't change anything about. Only criticism I have is that flanking bonus skills are useless on it so if I could I would change some of its skill tree. Flank on an archer... lol pointless.
10. Hunter, honestly I don't really like this class at all. Poison/toxic is ridiculously useless (worse than blizzard) and stealth is meh. It's bomb doesn't do damage enough for it to be worth it. It's basically an archer without longshot which in my opinion makes it bad. If anything this class needs to be buffed.
11. Alchemist is freaking terrible compared to assassin lol, I hate this class more than I hate hunters. Poison weapons and toxic cloud is as worthless as blizzard is. The only thing it has going for it is to spam shadowstrike or twin fang with flask of fire but so what? May as well play assassin at that point. Shadowstrike also has some big problems. It doesn't reset the cooldown of stealth and its range is ridiculously short. Shadowstrike needs a bigger hit radius because its way too damn short and misses way too frequently. Poison weapons and toxic cloud need a massive buff. They are totally useless. Spamming bombs is weak as hell as well, I've done it with two red birth blades and it just seems weak.
12. Templar, wouldn't really change anything about it other than giving it bonus XP for when it uses horn of valor. They don't generate much xp in a group at all. You buff your allies but you gain no xp for doing it. That is kind of lame and i always thought it was lame. The class itself is not that amazing in perilous either. Most of the time groups of enemies in perilous die before the templar can even get a decent dispel combo off anyway. I think its a balanced class for the most part. Horn of valor not giving you any support xp is really lame though. If someone gets a kill with horn of valor on them it should give the player who is playing the templar some additional XP. They just don't generate good XP compared to other classes in perilous difficulty.
Anyhow that about sums it up. Also there are various rings other than static cage that do not stack when you use two of them and some of them don't even work properly at all with just 1 of them. Rings are way too buggy and they need to fix them.