Except when it lead to ninja looting, resentment around favoritism, precieved or otherwise. And made split excessively efficient for bleeding edge raiding guilds.
Personal loot is the simple and straightforward system. Either you get something, or you don't. If you get something and you don't need it then you can trade it. The problem you have seems more rooted in how the game decides what you do or don't need. Which is a change that could be made without having to return to ML.