Bash + coreutils is powerful. Putting that on windows is a very good thing. The "performance increase" is irrelevant compared to the ease of use, available documentation (man pages), interoperability, and maturity.

It's worth noting that the traditional UNIX text-based utilities are designed for reporting to a user. Using text to generate reports is the most intelligent thing they could have done, because humans universally process text. It's not a superior programming environment, but it's a superior reporting environment, which is helpful when you're trying to reverse-engineer some third-party ELF binary or debug why your shared memory object sometimes causes clients to crash. That we sometimes take strings from our reports and pass them into our shell is accidental.

The same can be told of the REPL environments of Smalltalk, Interlisp-D, Lisp Machines, Mesa/Cedar and Oberon.

All more powerful than UNIX shell languages while using structured data.

Coming from Spectrum, MS-DOS and Amiga, the UNIX shell seemed powerful until I discovered how the development workstation should look like, from the eyes of Xerox PARC.

At which point you switched to emacs and never looked back? (-:

Amiga REXX should have militated against that view of Unix shells slightly.

the biggest problem with bash on windows is that it has poor interop between Windows tools (to the point of almost no interop). In that sense, cygwin is already better than the recent Microsoft offering.