Yes he has, his defensive stats are much greater than johns. And stones has made just as many mistakes as funes just doesn't get pulled up on them because he can do no wrong in some people's eyes.
Johns class and will probably be the best of his generation but at the minute he's found wanting defensively at times, he's been the weakest link out the back 4 over the past few weeks needs a few games out to ground him again
I'll admit Stones has made mistakes mate, but he also makes a lot less when Jags is next to him.
Mori has done well, and I've been impressed, but he was brought in as a third-choice CB, at least for this season. He's proved he's capable of stepping up though, which is a good sign.
For me, it's just interesting how fans/pundits react when a young player goes through a tricky spell of form - which Stones is now doing for probably the first time. There always seems to be two camps (usually with the same people in each of them).
A - Calls for them to be dropped (a kick up the arse etc/needs a rest). This happened a lot with Lukaku last season, and even more with Barkley (this season, even though he's been one of the best midfielders in the league).
B - Leave them in, let them grow and develop and overcome this bad spell - as it will make them a better player overall. If the mistakes continue for a sustained spell (e.g. five, six games) then maybe look to switch it up. (Basically what Rio Ferdinand said on 5Live last night).
IMO, Option B is preferable, but then again everyone thinks differently.