Aside for the fact that I find an aprioristic hate for cooldowns a bit ridiculous in principle (there's nothing about a "cooldown-based" system that is inherently worse), I'm not sure why this is even a question when it's D&D we are talking about.
D&D doesn't use cooldowns. It has item charges and limited numbers of uses per day.
The problems with cooldowns :
1 - MAkes no sense. Except in few ocasions. Red Orchestra machine guns overheating and you needing to wait cooldown or change the barrel is the unique exception
2 - They homogenize the combat into the same rotation spam
3 - They make you focus more in your action bar and less in the action. You are trying to use the max DPS rotation instead of figuring out what spells are best for the situation
4 - They break my immersion
5 - People only accept this BS on RPG's. The new contra added CDs and everyone hates it(with reason)
6 - They slow down the gameplay
7 - They make character progression less impactful.
I don't see a single vantage of this mechanic.