The problem here is that Fr. Jenkins is raising his opinion to the status of dogma, inasmuch as he says that people who go against his analysis (dogmatic sedes) are not traditional Catholics. It would be reasonable to say he disagrees with them or that they are wrong, but by saying they are not traditional Catholics he is usurping authority he himself does not have.
I did not take it that way. He said: "I don't even consider those people to be traditional Catholics at all, because they are usurping authority they don't have".
He is correct, they are usurping authority that they don't have, which is something that traditional Catholics simply don't do.
He is saying that dogmatic sedes continue to insist that their opinion is taught by or is a teaching or part of a teaching of the Church - even after being corrected, those who do such a thing he does not consider to be traditional Catholics at all - he has this opinion because it is something that traditional Catholics simply don't do, not because it is a fact or certain. He is only offering his opinion, not making an official proclamation. As such, he is not usurping any authority.
He is only offering his opinion, because he says "I do not even consider", he does not say "I'm telling you they are not Catholic", nor does he site any canon or teaching, nor is he in any way communicating that they are in fact, positively not traditional Catholics.