48% winrate is a ton better than plenty of other toplaners. He's super popular - which means more people with 0 clue how to play him are using him - compared to other LOWER winrate champs that are rarely being played (except largely by EXPERTS) and they STILL have low winrate. Those are the champs needing help; maokai is more than fine. When maokai loses, chances are it's because his team fell too far behind and deal 0 damage - meaning he can be as tanky as he wants and it makes no difference, since there is no damage to back up all his durability and cc. That's not a sign maokai is weak and needs buffs.
While I don't believe pro's know everything or know best all the time (I've innovated things before them sometimes or known better than them), they generally have a good clue of what is at least PASSABLE as a champ. With all the maokai being played - clearly he's not some weak champ that's a liability for his team. He is perfectly fine as-is.