You might want to look into some. There is one on wizard spell list that gives +5 to might and intellect and that is HUGE buff to damage and AoE for you. You can make it auto cast at start of fight pretty easily.
That's bad point. POE1 still have limit on the number of spells that you could cast. Only real difference is that you don't always have "spell for the job" on you, but spellbooks kinda negate that anyway.
That doesn't fix it, really, as you still kinda need to test spell in combat to know whether it fits you. If all you wanted is for player to learn spells gradually, then just change it so they get to choose a new spell per level
Multiclassing is concern, yes, but then instead of spells you could just have something else to spend your skill points on. In case of wizard it could be extra memory slots so you could choose to be more versatile in combat vs putting more points into other class.