So what would you have the WT do? Serena Williams is off the scale as far as a typical Witness goes. She can say what she likes and the WT can't do a thing about it. I'd be amazed if she's even associated with a congregation. When was the last time she attended a meeting? Can you even imagine the elders trying to speak with her, arrange a shepherding call, ask for her report?
I'm no WT apologist but trying to use Serena Williams' hypocrisy as a stick to beat them with seems silly. I've never met a Witness who takes her seriously as a JW. Most just say Jehoober knows her heart and it's up to him.