Correct: Doug's Re-Embed Artwork Script is the best current solution
It's currently at version 3.1 updated August 25, 2020 for those of you who installed a version before that.
I finally got a reply from Doug after asking him what his script is doing to the artwork such that file sizes are sometimes the same after running it, but often times smaller and sometimes larger.
He said he had no idea.
Which seems... odd... but I put this out there to ask others who are pedantic and have used the script, to let me know what their experience has been.
Are your file sizes changing after running it?
Are you noticing any size or quality changes to your embedded artwork?
Also: for those looking for an iTunes alternative, the best solution by far that I've found is to run your own Plex server and then use the excellent PlexAmp app for playback on your devices.
Yes, this requires running a server, which might be a non-starter for most people (Plex is super easy to use, but not everyone has an always-on/always-connected Mac to dedicate to this) and, yes, you'll need to invest in a Plexpass, but the experience is really fantastic now (I bought a lifetime pass ages ago for about $80).
All the keyboard shortcuts you'd want are built-in to the Mac app (including star ratings!) and once you get used to the unconventional UI you might decide like I have that it's really quite clever. Or you can have a more typical experience using your Web browser for Plex.
The iOS version of Plexamp is excellent, as well. If you don't like it, there are many other media players (like Prism for iOS) that can also hook in to your Plex server.
And, best of all, you have native FLAC support with Plex, which ends up making iTunes seem like a music player for elementary schoolers, which seems to be Apple's target demographic for the UX of most of its services now.
The one downside to Plex is that while it can import iTunes playlists, it doesn't seem to properly migrate star ratings (search Google for more about this). I haven't done a deep dive to figure this one out yet, though.