This works very well for tech enthusiasts and people who self-host nextcloud at home.

The issue is when you are a government or university, it becomes harder to get all your users (which are probably not all tech savvy) to install a third party app store deal with the Android warnings about installing from third-parties, etc etc.

And this is probably the user base Google are targeting with this move (assuming it’s malicious) . When the higher ups complain that their files are not syncing and need to install things with a special procedure they sometimes wonder why they are not using M365 or Google which seems hassle free.

To answer the last part of your post:

So far my experience is that the RCS-iMessage feature is working (or not) depending on the Apple user’s provider. I’m on Android with a “cheap” provider in Canada and RCS-iMessage work with my iMessage contacts that are on major providers but those on cheaper providers don’t work yet.

So if you are on Android and your basic RCS works you should be good.