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