Given how decent a company Valve is, and the rules they put on things for sale in their store, I'm honestly surprised that Valve even has store terms that allow this kind of shenanigans.
If I was them I would lock that down, because this is a bad look.
Ubisoft seems like an outlier on Steam. The way many of their games just launch UPlay, which then does its own downloading and ownership check is very strange and awkward.
Valve's rules are pretty permissive, all-in-all. And like many other people in this thread have already pointed out, many digital-only games can't ever truly be "owned". You're given a license, and that license is subject to terms that you agree to when you use it. It sucks, but this is the path we chose when we decided that software should be a proprietary production.
Valve tends to be pretty decent. If I had to guess, it’s cheaper and easier for them to say “yes” and let public opinion turn that into a no than to say no being the scenes and have to dicker with Ubi lawyers.
If I was them I would lock that down, because this is a bad look.