I don’t think he’ll ‘ruin’ anyone. He didn’t do Maguire & Robertson any harm for instance. If a player is good enough they can still shine through his shit.
Maguire only broke into the team when Bruce packed the pip and bailed on the eve of the season after they were promoted - before that Bruce had him firmly on the bench even in the Championship.
And even if he played Robertson, it was more of a punt from Liverpool on him. No big fee transfer, no other big clubs interested. I don't think Liverpool ever intended for him to be anything but a back-up player.