On their website it says they haven't fully ported over ActionScript yet, but once they do, wouldn't that mean all games should work just fine on this site?
Unfortunately, no. The Ruffle team is doing great work, but it's a hard problem with 1000 exceptions and fringe cases to handle. If what you're asking was true, then all of our ActionScript 2 games would be available on the site. But, only some are.
The reason for this is that while most, if not all, of our ActionScript 2 games "work", in that they load, many of them do not play well or at all. The same will be true, if not even moreso, when ActionScript 3 becomes part of Ruffle's functionality.