This is one of those situations where Table Top doesn't translate perfectly into a Videogame.
"Set ability to X" items are more powerful/build-defining in Single Player Games with no loot randomization because you can meta-game it much more easily. The other issue is due to a design choice by Larian. With no item attunement system in place, the game will revolve more around magic items because they can contribute so much more to a character's power.
It probably won't break the game for most normal players, but we'll probably see a lot of min-maxers or speedrunners dump certain stats and rely on these items instead. This existed in BG2 also (ring of human influence, STR belts), and I don't think it was too disruptive, but it does force optimization towards certain metas.
As I previously mentioned... you can meta-game it EXACTLY the same playing in AL. Direct translation from tabletop to CRPG in this instance.
As for the attunement issue... this is yet another mistake Larian has made (imho). The game (5e DnD) is balanced around the majority of magic items requiring attunement and thus leading to decisions on the part of the player as to what items to stack on their character. Simply not implementing attunement is basically the equivalent of them not deciding to include concentration... we're rushing back toward the 2nd edition days opposed to faithfully implementing 5e. Solasta did it easily enough. I'm not seeing the upside to ignoring attunement.