I don't think Toni is the problem
I am not even sure anything mental is Nadal's issue. like, for example, in the first set today Nadal was getting insanely outplayed yet managed to make it kind of close.
the real issue is that Rafa has been grinding his body down for a decade+ on tour and he's physically declining, unable to last as long, run as fast, hit as hard. people were predicting that he'd decline or be out of the game by 25 and he managed to last a lot longer than that
I expect Nadal to still get some big wins but its not a shocker that he is playing worse at this point in his career, and I certainly don't blame Toni