Eliminating single entity would require the league to go into collective bargaining with the players regarding a salary cap - they couldn't just "set" it. You don't really give any reason to eliminate single entity - I see no reason that teams couldn't be allowed to buy and sell players at will under the current arrangement. Trading a "discovery pick" or an allocation for a player is essentially the same thing already.
Well, since the collective bargaining agreement is already in place, including the cap, why not allow more individual control now?