You know that it is still rng to even recieve a Item with personal loot yes? You're not just handed an item every time you down a boss or do something otherwise stupid. Imagine being a niche class which needs one specific item that isn't dropping for everybody, your chances on getting hands on that item will be very very low, lower than they'd been before the complete personalization of loot. Imagine being a class that needs a specific item to be viable in the current mythic level of a raid, since the raid just released its heroic version people have low item level, now that Item which you'll undoubtly need drops, but not for you, but instead billy who doesn't needs it, he can't trade it to you because a) he hasn't gotten baseline ilvl in that slot or b) it forged. You're more prone to rng fucking with you than ever before.
BiS was a goal as any other in a game. Do you play this game without setting goals? One of the best things were getting that BiS Stuff and being able to not worry about gear anymore and therefore stop grinding and just do stuff you've wanted to do.