Kinda disagree on that. Forgetting the comparison between BG and DOS, I think that 5e is severely lacking in magical items, and BG had hundreds of those, and the most memorable items in the game are the craziest ones like Crom Faeyr and Vhailor Helm. There is a tradeoff between balance and fun, and whilst Josh Sawyer often chooses balance (a consequence is PoE2 having some of the worst gear in all RPG), I hope Larian chooses fun.
Yes, put crazy OP shit there in the optional dungeons, this is how the BG games did.