If he had a controlling interest, he would have gotten what he wanted right now, which is for AOL Time Warner to split up. He has been denied several times for things he demanded. The most notable was when they sold his beloved wrestling organization to his publicly hated rival Vince McMahon, but not before embarrassing canceling the wrestling show on his own network TNT and TBS.
Since he has sold of a most of his shares, he is now attempting to buy back the atlanta braves, whom he did own, and now belongs to AOL Time Warner. If he "owned" AOL Time Warner, it would be mighty odd to try and buy assets that he "owns" from it.
He also had the indignity of having been denied when he demanded CNN hire a friend of his, and they refused. His relationship, with Dick Parsons, is at best warm, his relationship with Steve Case, horrid (he has threatened him on several occasions).
Owning shares in a company, and owning the company, are 2 different things, the fact that he could be fired or be able to resign shows that.