Thanks for the extra info, that really helps.
I'm a Canvas admin myself, so I totally understand the frustration around issues like this where things seemed to work fine previously and you one day find everything suddenly in shambles with no warning. When that happens you have to try to prove to people that there was actually a change, because you can't really go back to the way things were X days ago in Canvas. I shall join your vent on this one!
As I mentioned, we have Kaltura for media, at my institution, and we went that direction because we noticed early on that uploading media content to Canvas files was resulting in suboptimal experiences for users. As you noted, the playback experience isn't great, we had audio/video out of sync, playback that would just stop in the middle of longer videos, there are no captions, etc... This was almost 10 years ago, and I know changes have been made and not all of those issues exist anymore, but I really feel like having a dedicated video platform is better overall than relying on Canvas. Should Canvas be better at this? Probably... But media is very complex, and I know there are only so many development resources to go around (sad but true).
If you have Canvas studio in addition to Canvas LMS, I'd probably encourage you to move as much of the media as possible from Canvas files over to Studio. I think you'll likely get a better playback experience (though maybe not exactly what you want, I'm not exactly sure), and things will be more accessible for students too, which is super important if you're in the USA with the Title II changes coming in the next couple years. It may even solve the rate limit issue, though I can say even with Kaltura, we occasionally get "access denied" or other errors when there are a large amount of videos embedded onto a single page (or discussions where students all post their own video responses).\
Please do feel free to continue the discussion and update the community with findings if you get to talk to your CSM about this!
-Chris