Do you have a particular reason to want emacs from MSYS2 rather than a Windows build of emacs (winget install GNU.Emacs, I think)? I’ve not tried it, but if the comparison with Vim-for-Windows is anything to go by, it at least removes worries about line endings and path translations from the equation.
Otherwise, is anything in Tuareg/Merlin on Cygwin of help? (similar setup, just with Cygwin)