I'd agree with all of that except the part about Stones. A lot of their key players over the last few years are the wrong side of 30, especially in defence and show signs of being on the decline and arguably they haven't been replaced by better, younger players.
For Stones, I think he has the talent and potential to be one of the best defenders in the world, but possibly not for another 3-4 years. His mistakes seem to be related to either trying to overplay or due to a loss of concentration. These are things that can be improved on with experience and coaching. I suspect that if he was playing alongside a fit Vincent Kompany, who could talk him through games, he wouldn't make quite so many mistakes.