If you have ever worked with both there would be no question.
They're different approaches and the only real benefit of bash is that it's super entrenched and extremely widely supported. With the same level of support Powershell would run circles around it. But since we're comparing things in the real world, Powershell is roughly equivalent to bash for most tasks. Better for some, worse for others.
I'm not sure what you mean with this.
If you're referring to feature set and robustness with typing in scripting, I might agree with you.
I have however a much tougher time agreeing if you also think that powershell could come even close to bash/zsh when working from the shell, in both speed of use (and as you said) support.
At the end of the day, both bash/zsh are "dumb" shells, they don't have the introspection capabilities Powershell has regarding commands they execute. That's both a benefit (they're flexible and you can throw anything at them) but also a disadvantage (they can't really help you much out of the box when you want to run a command; they are only able to help you regarding things they find out from the kernel, such as files, but not arbitrary info from the commands themselves).
The reasons that bash/zsh are faster and better supported boil down to history: tens of years of production usage by millions of people. As a result there's this cottage industry of tips and tricks, autocompletion scripts, etc. that makes bash and zsh usable.
I'm willing to bet that with a similar amount of man-hours poured into its ecosystem Powershell would beat both of them.
But as I said, we live in the real world and both bash/zsh are faster and a bit more robust than Powershell.
What exactly about bash would you say makes it superior?
In essence, the speed when working in it (compared to powershell). While powershell does have more features, at that point I'm just more likely to use python or similar for portability.