The purpose of lowering the number of spell slots in 5e was precisely to limit the power of high level spellcasters. They're still powerful enough, it's good.
Control spells need to be un-nerfed in BG3 though.
I am not in general against the simplifications they did in D&D 5e but they took away many options in creating your char. So i still prefer the PF rules i got in WotR although there are many things i do not like to. Especially the buff orgies before hard fights. So like you suggested if they un-nerf some spells in BG3 i will be satisfied.