I agree - I think even the 2015 MSN version that was so highly praised wasn't a patch on the peak goalscoring version from earlier.
But also - the loss of pace and explosiveness that @Gehrman talks about is a real thing. It affects everything, not just getting past players - he makes bad decisions about dribbling vs passing because he still hasn't figured out some of the things he can't do. His shots get blocked a lot because everything is one percent slower.
He's started from such a crazy level and technical basics (which Ronaldo doesn't have) that this diminished version can still do damage. But it's hard to imagine 2022 Messi having the same impact on the World cup as 2018 Mbappe or 2006 Zidane, but that's what seems to be the expectation now.
I don't think Mbappe 2018 was that great to be honest. Zidane was in 2006 but Messi definitely has that kind of performance in him. He's probably still better than the best version of Zidane becuase he's just as much of a creative beast while scoring much more than him and being a more proficient dribbler. As you said, Messi is held to the standards he set himself in his younger years. And everybody would fall short against that benchmark.