

It has standard bash capabilities
Well, ya. Its terminal interface, I’d expect it to have “basic” capabilities.
also can run standard dotnet libraries.
That’s not exactly a selling point.
What can bash do that PowerShell can’t?
Write succinct and easy to read commands. Interop with all the powerful tools in the Linux ecosystem (which is the point of a shell like bash).
posix lost except insofar as it lives on in the two mainstream highly proprietary OSs.
That’s just simply not true. Three majority of core utils you find on most Linux systems are POSIX compliant or mostly compliant. IIRC all the GNU tools are POSIX.
Vim (and NeoVim) are as much coding environments as VS or JetBrains. The difference is in the defaults.