In fact, didn't the SSPX clergy write an open letter in 1988 saying they were proud to be excommunicated from the Conciliar Church? If JP Deuce was the true pope, then certainly those excommunications were valid. It's a crime to consecrate bishops without a papal mandate and especially so when it is against the expressed command of the pope. Unless there is a sede vacante and there is an urgent need for new bishops.
Supposedly the big problem with the SV position is that 60 years is too long. But there is no dogma that a long sede vacante contradicts. Whereas resisting the pope is certainly contrary to dogmatic Church doctrine concerning the papacy.