A local minimum is a point in the design space from which any change is an improvement (but there's other designs which would be worse, if they make several larger changes). I think it's hard to make that claim about Git. You're probably referring to a local maximum, a point in the design space from which any change makes it better (but there's other designs which would be better, if they make several larger changes).

In my career, I've used Svn, Git and something I think it was called VSS. Git has definitively caused less problems, it's also been easy to teach to newbies. And I think the best feature of Git is that people really really benefit from being taught the Git models and data structures (even bootcamp juniors on their first job), because suddenly they go from a magic incantation perspective to a problem-solving perspective. I've never experienced any other software which has such a powerful mental model.

That of course doesn't mean that Mercurial is not better; I've never used it. It might be that Mercurial would have all the advantages of git and then some. But if that were so, I think it would be hard to say that Git is at a local maximum.