The major issue is that, if your deck can support a companion without sacrificing anything... then you run it. Lurrus is just the best of em.
Maybe I am alone here but isn't Lurris kinda top tier playable without having to be a companion? Recall that there was a discussion when she first came out as to if it would be better to have 4 copies main deck than 1 as a companion with the restrictions. There are a few cards, notably Monastery Mentor, that you would very likely like to run along side her.
I think the new companion tax is enough that it will remove that strategy from the meta outside of decks that already conformed to the deck building requirements, but as a maindeck player in something like standstill? That's still very strong.