The only fundamentally different thing about companions are that they are restriction-proof.
No, SOME of them are restriction proof. Lurrus and Lutri are the 2 companions that have the distinction of restricting how many other copies you can play in your main deck, and just so happen to be the 2 that are most obviously vintage viable. All the others can be played in multiple and in the case of Gyruda it is actually pretty fundamental to the cards function. There is nothing about the companion rule that makes them immune to restriction.
For the past 27 years magic has been a game played by drawing 7 random cards. Gaining access to an 8th known card that cannot be interacted with is fundamentally different.
A) Drawing 7 random cards has almost never been the way the game is played. There have been I think 4 different mulligan rules since the dawn of the game and the printing of serum powder, plus the introduction of the play or draw rule. Best argument you can make is that a 7 card hand has been the starting point in magic, but it certainly has changed multiple times.
B) All the companions can be interacted with. They can be countered. They can be named off meddling mage. You can play a card like Drannith Magistrate. Void winnower affects a few of them. These may not be the interactions you want, but they are interactions all the same.
If every one agree that Lurrus is broken then i see no reason to wait. Ban it as compagnion and do not let the few vintage players left in the world struggle with an biased meta.
Not everyone agrees. I have some confidence it will be banned regardless of what everyone or anyone thinks because it is the easiest way to deal with the perceived problem some people have, but just looking at this thread you can see some dissenting voices other than my own.