Yesterday taught us nothing about John Stones that we didn't already know. Or that City didn't already know when they bid £50m. Or that Everton didn't already know when they struggled to impart any kind of positional sense on him.
All the potential is there, he may need longer than others to mature, that's not unnatural. The fee will hang over him however. Mainly because you can name half a dozen or more centre halves, his age, who are better and would've been cheaper to acquire.
Also, he comes across as cocksure, both on the pitch and in interviews. I'm all for confidence, but he has the air of a guy who has let the hype around him, go straight to his head.