(though I don't think wizards are overpowered even with every their spell ready) OK, let's invent a reason to bring other classes in.
* Make a quick-menu option to change a character. Your mage is out of spells? Change him to ranger. A locked door ahead? It's time for your thief. A boss? Check his stats with a character with lore, bring a suitable characters to fight him. * Make a reason to switch to other characters for non-casters. It can be fatigue, it can be encounters sequence where some characters will be more effective than other. * When all characters is tired / without spells it's time to do a long rest. There can be something to prevent long rests when there are unused characters from last day.
That’s because we are stuck at level 4. Wait till wizards can toss fireballs at will as you propose.
Or how about Larian tries to emulate 5e rules as much as possible since it’s pretty balanced instead of creating a whole new type of game?
