... my point is that it WOULD be infallible if one assumed a legitimate pope. I really don't understand why it's that difficult for you.
No surprise here, but you did not answer the question, I already know what your point is - it's ridiculous.
I think the reason you have no understanding, is because you are in a self inflicted conundrum, i.e. believing your "new theologians" in spite of reality.
Simply.......
If you actually believed the "new theologians'" teachings as regards infallibility, councils and etc., , then, like the rest who actually believe them and on that account, actually abandoned the true faith for the new faith, you would be a card carrying NOer. But, because errors and heresies that certainly have come from the conciliar hierarchy of and since V2, clash with your beliefs attained from new theologians' teachings, you are left in the state of another casualty of this crisis which you have dubbed, "sededoubtism". IMO, this "position" would be more correctly stated as being a problem to solve, not a position to be content with.
Reality shows there was a *true* council with a *true* pope and [nearly] all the bishops of the world - and from it came forth error. That is reality.
Reality shows that the pope and council were not infallible. That is reality.
Reality shows that popes and councils can teach error and when they do, [our faith teaches that] we are not to follow them - (those who don't follow them are commonly called "traditionalists"). That is reality.
Reality shows that the "new theologians" ideas, wrongly passed off and accepted as authoritative teachings, are wrong. That is reality.
Debate, deny and argue against reality all you want, to do so you will need to deny reality and use the new theologians' teachings and misuse Catholic teachings (not necessarily in that order), the result of which leads to your "sededoubtism". To paraphrase 2V's sig - "Anything but reality".