That’s only true in GM (although she’s above Orisa now as well), and if you look closely, you’ll notice that Orisa, Winston and D.Va all have trash winrates while Zarya is at 57%.
And Zarya being behind Rein is not really relevant, they don’t compete with each other, they play together.
While I agree that Zarya doesn’t need nerfs, implying she’s bad is quite unrealistic. She remains in the top 2 tanks overall, even though GM stoutly prefers countering hitscans with Sigma/Ball.