This scenario is something worthy of being considered something that "ruins the console experience". It's literally taking away an integral part of the package that you paid for.
This is not. This is just existing in a constantly connected world.
1. You don't need to create an account to play SP.
2. Why exactly should you be online to play in SP?
3. Burner emails exist for a reason. Also, like... do people not unsubscribe from spam emails? I mean, I've had a "Ubisoft Connect" account since 2008 when it was Uplay and I haven't received a single spam email, since... y'know, I unsubscribed.
4. I mean, if you're worried about Ubisoft tracking how you play a game, by all means... be concerned. about them tracking how many times you beat up a rando pedestrian in Watch Dogs??? How many hours you wasted picking up all the tchotchkes in AC Valhalla?
Games shouldn't have patches, games shouldn't have DLC, games shouldn't have an online component whatsoever. We should just go back to 1992 when we didn't have start screens, consoles didn't ask you to set a time and date, the internet was an option and not something that could provide your console with beneficial content and updates. If your console had a patchable defect you'd need to get a whole replacement.
Why should anyone have to put a disc in a game console and have to wait 10-15+ minutes installing it before playing it, having to delete a game from finite storage space or register for anything in an internet-connected society?
Your argument is essentially "I want to be connected to the internet to play something I don't need the internet to play with." which you've also stated you can do, it just requires a loophole.
This is a nuisance, and I agree with that. Is it something that "ruins the console gaming experience?" No. That happened 16+ years ago when consumers collectively agreed that being online to play games was okay and a necessity for console gaming, or that paying $50+ dollars for an internet subscription, having to download patches and firmware upgrades, among other things was something we could live with. Why did we agree to having that? Well, as others have noted: There are benefits that come with those drawbacks.
The console experience was simple and unencumbered, now it isn't... and registering an account is at worst a 10 minute endeavor to sign up for something you'll only use for that game, and never again; that's on top of all the other stuff you already have to do to get to a launch screen for a game.
Sorry OP. I agree with the essence of your concern, but I disagree with the framing of it as something greater than what it is. It's annoying, but ultimately negligible.