That's why I hate DnD system... Why be a mage if you can't do magic? Ugh. Seriously, I went through PoE2 and then PoE1 and it was a nightmare for me. Omg how quickly I got bored of playing as a mage because of skill slot system. It was a real disappointment for me.. :< I'm willing to accept it, but I'll never consider it as plus. In my understanding, support and mages classes should do magic, not swing a sword or shoot a bow. Otherwise, how do they differ from archer or warrior in the gameplay? I almost don't see the difference because "oh yes, I have skills, but I can't use them, I need to wait for a special battle!!!".
That's a somewhat fair criticism but definitely exaggerated. You always have access to cantrips so your mage should really never have to swing a sword or shoot a bow. Especially since cantrips deal more damage than non-magic weapons at 5th+ levels. Additionally, past 4th level I've found that it's rare to actually run out of spell slots before a day ends. Sure, sometimes you have to be conservative, but in most fights you'll be able to cast at least 1 of each level of spell.
A cooldown-based system might work better for D&D video games; it'd at the very least be easier to balance resting, the classes, encounters, basically everything. But, BG3 clearly doesn't have a cooldown-based spellcasting system and not enough effort has been put in to account for fact that D&D classes are based around resting. Although...I guess Fighters' Menacing strike has been made OP and everyone can use spell scrolls?? But the latter doesn't increase the effectiveness of the Fighter class, it just makes all classes more like wizards.