I've always been worried about doing this, because so many of the CDs in my collection are limited edition or international, and info isn't available for these -- or worse, they track to something already in the Gracenote database that would overwrite all my correct custom tagging. It's the #1 reason I haven't signed up for Apple Music; I've had iTunes randomly decide to rewrite the album/track info that I customized for downloaded purchased music, and I don't want it to do the same to my curated library. So I rip my CDs and back up all my iTunes library/media files in iCloud, but store and play them locally on my iPhone.
Google will actually upload albums/tracks that aren't in their catalog, so I can still stream them. However the other issue you mention is one I have encountered. Sometimes it works in my favor. I have some very old CD's, and Google matches them to newer reissues that have bonus tracks. Other times it might not be a switch for the better... and as you say you end up with a domestic version when you want the international or limited version you own. Not honoring custom tags is another issue.
Fortunately it's possible to have it both ways.... you can sync music to your local iPhone storage and play it in the cloud so it's available from other devices. We have Sonos smart speakers in a couple of rooms, and can request music from our Google Play library without using the iPhone (or we can airplay anything from the iPhone as well).