It does let you run it without downloading any "games" btw. If that's not the intended experience they shouldn't make that the shortest path UI experience.
but fwiw, I just tried mineclone and at least the jumping physics were better.
That's been a long running debate in the community, whether the "MineTestGame" should be included by default anymore. At some point MTG seemed slated to be even discontinued as a project, but instead it got some fixes for outstanding issues and kept intact.
In my case, when I was starting out, it was a nice way to incrementally add game features only when I was ready for them, with MTG being the base to start from. So I have a bit of a soft spot for it.
but fwiw, I just tried mineclone and at least the jumping physics were better.