Drawing conclusions from as little as 2 games as to the better player/deck is extremely fault when each game itself has as much variability as it does in a game of Vintage Magic.
I'm not sure that is actually the point of a match though. We are not trying to derive who is the better player, and "better" is a very loaded and subjective term. We are only trying to determine who won. If we wanted to know who the better player was then yes you are correct, we would play a larger series, but in a world where we can quantify who is "better" do we want to play a game where the better player always wins? Not a very compelling reason for a lower skill player to want to join the game. In this regard some variance is welcome and needed.
The existence of companions in a format greatly reduces variation as there is no variance as to whether or not you have access to that companion. Imagine guaranteeing a land, or guaranteeing any other non-companion card. Companions themselves are just a very small subset of cards (literally 1 card in Vintage's case for the past month prior to this).
The addition of companions has no positive bearing on how good the mana in your opening 7 will be, as you are still drawing from a deck that does not include your sideboard cards, of which you had full control over in building. Players already have agency in this regard as they can choose which mana sources and how many they would like to include.
If smoothing out the opening hand and reducing the number of non-games was WOTCs goal, as it has been for some time, then companion does nothing to affect the first as you are still drawing 7 and no companion actually touches your mana, and goes a hell of a way for the second by ensuring you have access to at least one card that is relevant at some point in the game. The interaction Lurrus has with Black lotus could be argued, but there is still variance in that you need to draw lotus.
So companion does reduce variance, but just not in the way all the other moves have done in the past. It literally adds what is in-effect a new game zone for players to interact with. The point I am trying to drive home here however is that the printing of the Zendikar fetches, the new mulligan rule, the continued printing of differently named redundant effects, all these things have had a far more prominent and relevant effect on the games variance than companion has in my estimation, and it has been moving in that direction for some time.