The small size of the "modern" Salubri bloodline is due to a long history of being the odd-man out, so to speak.
Saulot, their antediluvian, was originally a mystic. He was the healer among the thirteen vampires of the third generation. He mostly Embraced people like himself, wise and gentle, with the intent of them becoming healers as well. Of course, for a creature whose very creation was via jealousy and greed, people that met his standards (and could withstand the Beast, something Saulot himself made his unlife's goal) were few and far between.
He spent a great deal of time away from the other antediluvians (who were gathered in what was known as the Second City). When he returned from his explorations in the East1, he had quieted his Beast via a technique/state known as Golconda. He also brought the discipline of Obeah, and through related mysticism the third eye became a mark of Salubri.
However, behind him came a line of vampiric demon worshipers known as the Baali. Despite his control over his Beast, Saulot believed these creatures to be an abomination and deserving of only destruction. One of his childer gave up healing and took up the sword to strike down these creatures - Samiel was the first true warrior among the Salubri.
During the Dark Ages, the two castes went down very different paths - one focused on healing and teaching other vampires to reach Golconda, the other on hunting down Baali. Saulot himself was prone to long bouts of torpor. Things went sideways for the clan as a whole when Tremere found and diablarized him - Clan Tremere was sort of the new kids on the block, and Tremere wanted the power and prestige of a proper antediluvian for himself. His childer had similar desires, and took to hunting down Salubri for diablerie to improve their own station. Always a small group, in the end, it did not go well for the warrior caste. They frequently threw themselves against the newly empowered and magically adept Tremere, and came out the losers.
The few warrior caste that were smart enough or skilled enough to survive eventually joined the Sabbat, effectively becoming antitribu. They used the support of the Sabbat to help them in destroying Baali and revenging themselves on the Tremere. Sometimes called Furies, they're bitter and vengeful - not the kind of beings Saulot would ever recognize as one of his own.
1There is an offshoot of vampires he created when he was in the East, sometimes known as Watchers (in contrast to Warriors or Healers). Unfortunately, I don't have a good handle on the Eastern vampire splatbooks; I never owned them. As I understand it, they're an even smaller caste than the two "main lines".