Alright, after further playing, will definitely say that while having an AoE skill makes the game INCREDIBLY easy, especially if you can get it on you Warrior/Knight, the game is entirely doable with just single target or movement focused abilities. Finding really that, more than just outright killing enemies, the core of the game feels like just trying to minimize how often enemies can hit you, and that largely starts with making sure the midrow dudes NEVER reach that midrow, or only are able to get off one cast of their ability, otherwise you're just gonna get overrun with tons of damage coming from everywhere.
Frankly, letting enemies hit your first rows, so long as they don't get to stay there is probably the easiest of all to deal with, if only because you'll very likely have not just one in the knight who can deal decent damage to this row, but either the ninja or the archer as well, since all of their abilities deal damage regardless of the region they're in, they just might not get a bonus effect (ninjas smoke bomb). Wolves are probably the biggest priority if any among the first row enemies, but, beyond that you can pretty much just let them through with some damage from the archer when you can, and focus on Archers, and then the middle row guys most of all after that, obviously making good plays around movements and enemy position when you can.
Getting an attack item of any sort too helps a ton in nuking bosses, or just generally taking out enemies in rows where you might not have the sort of damage you like from other characters and they are a priority. I'm of the strong belief now though that Restrain is perhaps the single strongest ability in the game, if only because it can COMPLETELY trivialize any boss fight save for the power couple, just because it forces all the other bosses into a standstill where they cant being using their unique mechanics to mess with you, and by the point you're at a boss (final ones in particular) all you really need to do is focus down them and win.
For example, I see a ton of people having problems with what I think is the double wiedling lizard boss that is multicolored, but frankly, I've never had issue with them only because I've managed to keep them hardstuck in the final/green row, or at worst blue maybe. If you can keep a boss out of their preferred zone they just become entirely irrelevant, and Restrain will basically allow you to do that with no problem. Also bursting down enemies behind them and then shoving them back a bit is useful where needed, assuming the boss doesn't want to be in the green zone of course.
All in all, while I do think there is some pretty poor abilities in the game currently, and two of the strongest overall in my opinion are probably Restrain and then Intimidating Gaze, most feel pretty balanced all in all to be honest. Even the the poison arrows feel fairly useful when you're willing to take more guaranteed damage over the chance of a crit, and don't have the first rows to worry about as much. Great ability to get at the start at least... and it also has the double bonus of dealing 10 damage NO MATTER where the enemy is located. In fact, if there is one type of ability to look out for more than anything, its on demand damage regardless of the zone, something the knight have very little of compared to the other two, but the flame strike does wonders in this regard, while the archer has the most options in this avenue, maybe tied with the ninja as all of hers from what I've seen aside from one or two get full effects regardless of zone. For those struggling, and when you get a chance to buy skills, I'd say this is one of the key factors to keep an eye out for, that and AoE in general as both can make your life MUCH easier.
Never pass up Intimidating Gaze, and NEVER pass up Restrain. Both can just outright win you the game almost assuming you're playing decently. I'd also suggest buying just a few powerful skills from the Dojo when you get the chance, then clearing out the item shop as most of those items can be incredibly impactful as well.