Well, at the time of TOS, Spock said, "Earth believes the Romulans to be warlike, cruel, treacherous..." That sounds like what the Vulcans were like before they embraced Surakian logic. Kor
Unfortunately, TNG (and really "The Enterprise Incident") put quite a different sheen on them. When we see the streets of Romulus in "Unification", they look to be a quiet reserved people.
I don't think ancient Vulcans (a probably warp-capable race) were any different from present Romulans or ancient Humans of the time. It's just that they had gone MAD x 1000, and started to listen to a Stoic philosopher who said "Let's just all calm down here, people!" The shared telepathic nature of Vulcans makes controlling ones emotions even more paramount, as you would be affecting communities. And the Vulcans we see in TOS and the TNG era are a recent innovation of Syrranites taking over the society after discovering the equivalent of the Dead Sea Scrolls x 1000. Before that, they were just a semi-military dictatorship for who knows how long, being puppetted by the Romulans.
The problem seems to be associated with the Vulcan's telepathic abilities. In TOS "All Our Yesterdays" Spock is influenced by the savage emotional nature of Vulcans from 5,000 years passed. MCCOY: Are you trying to kill me, Spock? Is that what you really want? Think. What are you feeling? Rage? Jealousy? Have you ever had those feelings before? SPOCK: This is impossible. Impossible. I am a Vulcan. MCCOY: The Vulcan you knew won't exist for another five thousand years. Think, man. What's happening on your planet right now, this very moment? SPOCK: My ancestors are barbarians. Warlike barbarians. MCCOY: Who nearly killed themselves off with their own passions. Spock, you're reverting into your ancestors five thousand years before you were born! So the emotions of those Vulcans were telepathically enhanced, amplified to the point where they could influence Spock thousands of light-years away. The telepathy created an emotional echo chamber. This fear was a definite possibility in the case of Sarek suffering from Bendii Syndrome in TNG: "Sarek" CRUSHER: There's a very rare condition that sometimes affects Vulcans over the age of two hundred. Bendii Syndrome. Its early symptoms include sudden bursts of emotion, mostly irrational anger. Eventually, all emotional control is lost. PICARD: I can imagine nothing that would be more offensive to a Vulcan. Their emotional detachment is the very core of their being. How would this affect others on board the ship? TROI: Vulcans possess telepathic ability. Sarek may unintentionally be projecting intense emotions onto other people, at random. So the danger wasn't just to Sarek. His telepathic abilities would influence those around him. They would feel his emotions. On the other hand, the Romulans seem to have abandoned their telepathic abilities. They are a genetic offshoot of Vulcans, but they do not appear to have any telepathic abilities. If they do, those abilities are not as enhanced, refined, focused, or controlled as in Vulcans. So the Vulcans appear to have used logic to suppress their emotions while maintaining their telepathic echo chamber. The Romulans, on the other hand, seem to have gotten rid of the echo chamber and kept their emotions.
Why assume the Vulcans were the "correct" ones in their little ideological war? The Romulans are...well...fine. Their problems are mostly cultural and political until their homeworld blew up. What if Surak was the zealot who overturned everything, convinced everyone to suppress their emotions, and went on a global purge to rid Vulcan of those who disagree? What if the Romulans were the refugees? Okay, I missed this post. Basically, this, but with explicit forced diaspora.
The Romulan Way of Life could be a relatively recent development. They had 2000 years to become who they are, and may have begun as more democratic, peace-loving hippies. Vulcan was destroying itself by fighting telepathic wars (and atomic ones, of course), and two schools arose: The Surakians, who wanted to keep telepathy but stop using emotions to attack people. And the "ones who marched under the raptor's wings", who wanted to keep emotional states, but throw out the telepathy. Since telepathy is a pretty powerful tool, it's pretty obvious who would win and get exiled in this situation. Spoiler: Picard Spoilers ...and maybe they were both fighting against some advanced AI.
I found DeSeve's insight very intriguing: DESEVE: The Romulans are very moral, Captain. They have an absolute certainty about what is right and what is wrong, who is a friend and who is an enemy, a strict moral compass which provides them with a clarity of purpose. At one time I found their sense of purpose, their passion and commitment, to be very compelling.
Vulcan culture had strayed significantly from Sarek's teachings by ENT. From that standpoint, TOS and beyond, Vulcan is undergoing something of a reformation based on the finding of the Kirshara. Even then there were still factions, like Logic Extremists.