Nothing in "All Our Yesterdays" establishes the tech level of these barbarians, though. Perhaps in 3000 BC, they are meat-eating, brother-slaying barbarians with antimatter projectors?
Also interestingly, we never learn when the Romulans began to be called Romulans. Was that before or after they left Vulcan? "Minefield" establishes that T'Pol knows the name "Romulan" from old Vulcan history, but we don't know how old; "Balance of Terror" establishes that Vulcans had a barbaric colonial period, but we don't know if this was before or after they started starfaring, and whether it had anything to do with Romulans, or merely serves as an example of how bloodlusty an "unreformed" Vulcanoid culture can be.
For all we know, Romulans were one of the many factions that fought each other on planet Vulcan back in the days of brutality - possibly over racial issues, the "Romulan faction" consisting of the ridgeheaded race plus their smoothheaded sympathizers. Their departure from Vulcan is not well documented in canon; perhaps they did not really leave in disgust when Surak took all the joy out of being Vulcan, but rather were forced out by racist smoothheads? The ENT dialogue between Archer and Surak's katra vaguely supports the idea that they only left after Surak's own life ended, but perhaps the Surakian reformation and the associated Romulan departure only came centuries after Surak himself?
Adding to the mix, Q once discussed a hundred-year war between Vulcans and Romulans (VOY "Death Wish"). Alas, we don't know if it was in the past or the future of the episode, or perhaps in another timeline altogether. Nothing in canon precludes Vulcan/Romulan conflict after the separation as such; it would merely imply that a massive coverup existed so that Vulcans in the TOS era could still claim deadpan that they did not know for certain who the Romulans are. The aforementioned ENT dialogue almost establishes such conflict before the separation, but neglects to explicitly use the name "Romulan" there.