In fairness Bash can do that as well. It's not a shell specific thing, autocompletion is just a shell script after all, the issue is whether someone has written those scripts (which they have for Bash) and if your package manager ships them (which some do but others do not).
However I do agree that Bash generally feels outdated these days. In fact autocompletion was the primary reason behind me writing my own readline API
In my experience, this is partly true but in general it’s hard to get it to work well and in the end zsh is more slick. Xonsh is another shell that also has better completion than bash and with even less effort. (It’s not as stable though...)
I agree that there are plenty of shells which make it easier to write completion scripts (even I've written one which would fall into that category) and there are plenty of shells and 3rd party libraries which provide a nice UI/UX for autocompletion than readline does.
...however Bash can still do the items you'd described earlier. In fact back when Bash was my primary shell (which is a few years ago now), it literally did do those things you described and it came already pre-written as part of whatever Linux package I was using. ie I didn't have to write those scripts myself.
But yes, I do agree Bash is pretty horrible at writing and using autocompletion compared to more recent shells. There no doubt about that :)
