I'm reluctant to post in this thread because I'm obviously biased. It's hard for me to trust my own objectivity in this matter, so I accept that it would be much harder for someone else to.
I'm a little surprised how many people are just accepting that this is an ethical problem and jumping straight to a discussion about enforceability. I might just be compartmentalizing, but I don't see it.
I understand why someone would be upset to lose to a team of vintage players when they don't have access to a team of vintage players. I also understand why someone would be upset to lose to someone who could afford expensive cards when they didn't have access to those cards. This is unfortunate, but it's not cheating and it's not unethical.
I'm reminded of "cheesy strategies" from Sirlin's Playing to Win, and a tournament I went to once where the TO thought IDs were unethical and required everyone to play out all of their matches. When a ruleset is agreed upon ahead of time (which is what you're doing when you pay your entry fee), it's hard to argue that playing within those rules is unethical ... with the exception of things that would be unethical in any context, like physically threatening someone for a concession. (here "collaborating to make effective decisions" is not something considered always unethical). By the rules as we can infer from Wizards, MTGO is a team vs team game, where teams contain an arbitrary number of players.
It is, however, totally fair to decide that a given ruleset is unbalanced or unfun, though I think the term unfair isn't helpful here. This mindset gives us actionable steps and stops us from getting too mired in a fight over semantics. If the current ruleset - the one where WotC obviously doesn't care about team play, isn't fun, there are steps we can take to try and help. Player-run tournaments can have any ruleset they want, including "no teams", "no streaming", or "no streaming without a delay". We can ask WotC to clarify or change their stance on team play.
This is exactly why I campaigned to promote proxy-legal events back when they were unpopular 10 years ago. I felt that the official game, the one where most people can't afford a deck, was unbalanced and less fun because of that. Proxy Vintage is a player-run format with an similar but alternate ruleset that I personally find more interesting/challenging/entertaining (not everyone agrees with this, but not everyone agrees with any rules change).
For what it's worth I would no longer stream or play vintage online if Wizards took a hard stance on this. It's just less fun for me when I'm not playing with my friends or interacting with a stream - but that's fine, if the majority of players would be happier with a rules change, it's probably for the best.