I'm nearly 40, and am a lifelong sede. In full transparency, I admit that it is a difficult position to live with, since it is a theological opinion that merely provides a diagnosis/prognosis without providing a possible duration or cure. Only Almighty God in his providence can fix this crisis and restore apostasized Rome. I say this as a preface to explain that Sede Vacantism as not a position that I accepted purely based on my upbringing, but one that I struggled with and embraced anyway. I spent several years of my adult life questioning whether I believed this through my own intellect, or because it was what my parents believed. Like most sedes, I have aunts/uncles/cousins that are good and faithful SSPXers. I read many articles from the Angelus, open-mindedly read many forum posts, and ultimately came to my present personal conclusions over time, study and prayer. And no, I do not condemn those who do not agree with me or adhere to some dogmatic form of sedeism.
Having said all of that, I have enormous respect for Archbishop Lefebvre, and faithful SSPX-aligned Catholics. At the end of the day, we're living through the great apostasy and all trying to do our best to remain faithful to the Roman Catholic Church and save our souls. I pray regularly for unity among the faithful remnant in the world that the devil seeks to divide and to devour.
As to who we sedes got, I would say that Bp Pivarunas is a tremendous leader in this crisis. Unlike others, who although had admirable qualities and writings, tended to take their theological opinions so seriously that they bind the consciences of the faithful to their positions, Bp Pivarunas has maintained a very neutral, but very Catholic stance over the years. Although he and his clergy hold that the see is vacant, and do not say mass "una cuм", he does not claim that those who do include Bergolio's (or any of the other usurpers) name in the canon invalidates the sacrament, or that you are forbidden to attend their mass. Although he fully understands how bad and dangerous Bugnini was, and likely doesn't like the 1955 holy week changes, he and the CMRI maintain them. Not because they think they are necessarily good, but because they recognize Pius XII as a valid pope. And as such, are bound to follow what he put into place or signed off on, until such time as we have another valid and Catholic Pope who would change that. I personally don't agree with the opinion of others, that we can pope-sift and do away with things based on our own theological opinions or preferences. I believe we are to preserve and maintain tradition, not to modify and rebrand it as we see fit.
Bp Pivarunas helped to take the CMRI from a group of sincere laity led astray by a charismatic cult leader, to a well organized, sincere, and scandal free group that has grown and flourished under his leadership. They now have over 100 mass centers, over a dozen schools, a major and minor seminary, etc. They have countless hours of outstanding content available on YouTube from their annual Fatima Conference. And most importantly to me, they have managed to stay out of much of the backbiting and controversies that have plagued many other traditional groups, while charitably keeping a position that does not condemn or mud sling. I find that very edifying.
Finally, I'll note that I find it an interesting coincidence that His Excellency Archbishop Levebvre passed away in 1991, the same year that Bishop Pivarunas was elevated to the episcopacy. Deo Gratias