I have also found core to be difficult to use in some cases, but it is
a much better codebase in general than the 'compat' dumping ground,
and I am thankful for the people who have worked hard to bring it to
its current state.
It is close to being ready for general use. We need more people
trying it and reporting errors. If there are problems with
mwparserfromhell on Windows, we need to understand and fix the problem
in mwparserfromhell, and then properly set the dependency version in
pywikibot core.
fwiw, Betacommand is talking about this issue:
https://github.com/earwig/mwparserfromhell/issues/54
https://gerrit.wikimedia.org/r/#/c/138209
--
John Vandenberg