You can take a horse to the water but.. Difficult to make a ballbasher win in this field so what he does with Yastremska is not the yardstick. Yes, it is quite possible, even likely that he is no genius and just a pretty average coach. But do tell me how many tier 1 greats have you heard publicly slagging the coach in a presser? Not talking heat of the moment yelling like Murray but telling all the world that your coach is useless. Did Fed do it? Did Serena throw Pat under the bus even during the 2018 USO fiasco? Nope. Y'all erupted when Djokovic appeared to have been less than 100% superlative when he announced his parting of ways with Becker but somehow Osaka gets to tell the world that Sasha's tips are useless or common knowledge? It's not about her being young. Great champions already have a mindset that shuts out the noise and they understand seeding friction with the coach is not going to help matters so they shut up and play. Now who else throws his coach under the bus unrepentantly? Zverev, that's who. And how many slams has he won? Zilch. Look, the coach doesn't have to win a single match so the onus finally lies on the player to get the most out of whoever they work with.