While I take anything onscreen as canon, I don't agree that canon isn't subjective. It's always subjective. Paramount says, "Our criteria for what is considered canon is X" but anyone is absolutely free to say, "I have a different criteria for canon, and reject the Paramount canon".
It's like, ask a catholic what biblical canon is, and they'll tell you, "These books are canon". But you ask a protestant and he'll say, "These books are canon". If you ask the protestant if the catholic canon is canon, he'll say no, and vice versa. So, Paramount is like the catholic church, and fans who accept Paramount's canon-criteria are like catholics. People who don't accept Paramount's criteria are like protestants.
A catholic will say that the catholic church is the final authority for determination of canon, a protestant will disagree. So a person who says, "I don't accept TATV as canon" is saying, "I don't accept Paramount as the final authority for determination of canon."