Oh I'm not saying jj commands are 1:1 to git. But it looks very much like a convenience layer on git, which is supported by the fact that it (can?) use(s) git as its storage backend. So people are essentially commenting "that jj thing looks perfectly doable in plain git too".

Yes, that's correct. It's also correct to say that you don't "need" the Git porcelain commands because it's perfectly doable using Git plumbing :)