Utter manure.
I am a sedevacantist. I do NOT believe it is the "only" Catholic position to take.
As usual, you are wrong.
I am NOT sedevacantist. Or sedeprivationist. Or SedeBenedictPlenist.
Yet my experience with the aforementioned is pretty much what you say. Most sedes I know, regardless of the variety, do not take a hardline position that theirs is the only acceptable position for a traditional Catholic to take.
Not even the recently-deceased Fr Anthony Cekada, who I use to correspond with from time-to-time and who very kindly invited me into his rectory for tea, sandwiches, and cookies the first time I visited Cincinatti.