I'm happy to decide that on a program-by-program basis, and reduce external dependencies, where that does not increase my code's complexity. I already described a problem I ran into from using a wider selection of modules (and you'll see from correspondence in the past that I have run into problems with gnulib on a regular basis), and I also have to deal with complaints about the use of gnulib by downstream packagers and other developers (particularly on Windows, ironically!).
I'm interested in why you suspect MSYS would be worse than mingw? Is it because it is not as widely used as mingw and therefore the extra POSIX APIs etc. that it provides are not as well tested?