Simple answer is we need the Xbox app because Microsoft says we need it. The Xbox brand is more than just the console, and MS is consolidating Windows + Console gaming under that brand.
Is it technically possible for MS to create an installer that doesn’t use Xbox services? Of course it is, they develop the game, they can do whatever they like. The developers can create all manner of installation types.
Is that going to happen? No it’s not. They aren’t going to take a flagship game and break it out of the Xbox brand just cause some people are upset about seeing that “console” app on their PC. The Xbox app has some nifty features as well, such as the ability to play your Xbox games via remote streaming on your PC - you can play AAA titles on a low-end laptop that way. And if you don’t have an Xbox handy, there’s a lot of games on their Cloud streaming service that you can use.
So the sooner you accept that “Xbox” is not going away, the happier you’ll be. If you are really that concerned about bloatware, I would suggest that you need to leave the Windows platform and move to Linux. Even the Mac has started loading up things with their own shift to consolidate Mac + iPad. It’s just how things are now.
Linux + XP is still an option if you are simply not going to accept the state of things today.