But that's just Ubuntu with another repo added on top, with some different default package choices.
I would not oversimplify it as just "repo added on top". For many years we could say the same about Ubuntu and Debian, but I don't agree with this generalisation.
It may walk like a duck, but if it doesn't quack like a duck, it might not be a duck.
[0]: https://pop.system76.com/
[1]: https://blog.system76.com/post/more-on-cosmic-de-to-kick-off...
Ubuntu tends to fork Debian's unstable branch then freeze it, patch it, rebuild it and call it their own. Pop_OS! is simply adding some software on top of Ubuntu.
If Debian makes a change, Ubuntu is unaffected until they resync. They then have time to patch it and test. If Ubuntu changes a package, that change is immediate in Pop_OS! unless they ship their own version of the package.
I agree that Pop_OS! is doing a great job with their DE modifications and other defaults, but I don't view that as them being in control. Unless a lot has changed since I used it last, Ubuntu and their infrastructure is still building most of the distribution.
A lot of this is really where you want to draw lines in the sand. What makes a distro a distro and not just another derivative?
I can see why they are doing it, commercially, but it seems misguided. There are so many other ways they could bring value for corporate customers without trying to copy Apple/Microsoft/Red Hat.