I don't agree,I think he's looked a bit off since returning from injury.The other players you have mentioned are all subject to the same treatment IMO,no one is exempt.Unfotunately though we aren't as blessed in other areas.
I definitely don't see another Sane situation,he was just a fanny.
I don't have enough of an argument to really change your (or anyone's) mind here but I'd like to try anyway and suggest a counterpoint.
Laporte was not any worse after the injury. In Laporte's entire tenure at the club prior to his injury City were an absolutely dominant side, that very rarely failed to win. It was such a strong side throughout that everybody brought the best out of everybody. You can't say that about last season or this one (yet, hopefully). No outfield player looked as good last season as they did during the two seasons prior. Even the very best of those and most consistent (De Bruyne, Walker, Aguero) each had moments during games that exposed their weaknesses that wouldn't have been a remote problem back in the title winning seasons, if even noticeable.
Laporte came back into the team and in my opinion did everything he normally does. It's just the team was worse and so the things he got wrong became more obvious. But he was doing all of those things prior to the injury, we just didn't notice. He's always been a more subtle defender compared to some of the more crash and bang guys we have so it's less obvious as to the things he does too, good or bad. You could talk about his attacking contributions similarly too.
But as far as I'm concerned we went from a team that were haphazard and eternally leaky at the back regardless of opposition to a team that were solid and picking up frequent clean sheets after Laporte came back into the team. Across the season we got 10 clean sheets in 14 games he started. Post injury it was 8 from 10. And that was with the likes of Garcia, Otamendi, not quite right Stones, and not quite CB Fernandinho next to him. I think he was as good as always, and he had a hugely positive effect on us for being fit and as good as he was.
All that being said, it's good Stones seems to be stepping up, and hopefully Aké can too once he's fully acclimatised. 4 top CBs to compete with each other over 60 games is a really great thing for me. I know Dias is looking really good right now but there's no guarantees that he'll be 1st choice if the other 3 push hard, which I assume is the point.
tl;dr Laporte as good as ever, just mistakes were more noticeable because the team has become weaker than previously.