The question of cooldowns vs no cooldowns is probably moot. Larian signed a contract with Wizards of the Coast to produce a 5e D&D video game. I am sure that there are provisions to change some rules where needed for playability, but something like cooldowns would be a dramatic change to the structure of 5e, and there is really no way you could spin them as a playability change. I suspect adding them in a big way would go against their contract and get them in trouble with Wizards.
I am sure that Larian will eventually make another game in the divinity universe, and you will likely find cooldowns there.
