Let’s look at it another way: It puts a greater reliance on leeching and other possible recovery methods like on crit/per kill or just chugging potions and massive regen in general.
Like others, I agree that long cooldowns shouldn’t exist in a game like this, and tangentially, things like (de)buffs shouldn’t last a few seconds. However, the real atrocity is when you double dip a cooldown with some other cost. That should never, ever happen.
Otherwise, we also need to look back to why D3 initially got rid of more widely available leech mods and eventually added unavoidable damage. People didn’t give a damn about defense. As long as you could survive a hit, you’d just refill your globe on your next attack and the process would repeat. This sort of ping pong effect also existed in D2, which further had the virtually unlimited potion safety net. You can’t really balance content around the thought that people are going in undergeared, but also effectively immortal. Combinations like this are pretty much the textbook definition of overpowered. Sadly, D3 chasing infinite scaling through the GR system largely invalidated why they took those initial steps mentioned before as we eventually hit a point where party buff stacking and insane paragon became required to also survive multiple hits.
Fair lengths aside, I’d also stress skills have their costs and efficacy properly balanced. If players are going to frequently have 5-10 monsters on the screen, AoE abilities should probably be costing 5-10x as their ST counterparts and never doing as much per individual hit. If an AoE cooldown does 3x the damage of an MP-based counterpart, said cooldown should roughly correlate to the natural MP recovery of spending that other AoE 3x and not 90+ seconds. D3 had another problem where many classes’ builder phases were grossly underpowered, to the point people chased whatever method would accomplish infinite spending, typically through a mix of resource and cooldown reduction. Pragmatically, this was just another form of leech exploitation and also OP in its own way.
But what’s more important is to not go for breakneck pace play. This may run counter to those who think the game should eventually become brainless farm mode, but the above problems facilitate just that on top of hyper-mobility spam. There’s no resource management if you’re just spamming. There’s no tactics if you’re skipping fodder and just using AoEs, period. For those that look to this game and crave some sort of persistent challenge, you just can’t tolerate the above. “Well, just make a higher difficulty!” is not a solution, either. We’ve been there.