It being "just a wrapper around git" is an excellent argument that the user interface and usability are problematic. Nobody is arguing with the mathematical model underlying git. Gitless manages to expose a lot less state by default. That's a usability win. It's still there when you need it. There is no expressiveness lost. I find the examples they give on their website very persuasive:
If you want the detailed analysis of weaknesses of git that led to the design of gitless, it's here:
https://people.csail.mit.edu/sperezde/onward13.pdf
I don't necessarily agree with everything in there but I think it's an excellent analysis overall and worth reading as a case study anyways.
In my workflow I also see no cost, but I am happy to accept that that's because we don't have very sophisticated needs.
Now, if you have some legitimate gripes about git's usability I'd love to respond to them and have a real discussion, but Gitless doesn't make those arguments, it's just a wrapper around git (which could all be done with aliases) that adds an additional layer of abstraction for no benefit (or at least none that they've felt confident mentioning)