The Romulan Empire is , to my eyes, what Vulcan would have been had Surak not spoken his mind, so to speak.
While canon hasnt gone into enough detail about The Sundering to make any stance valid regarding how the current day Romulans/Rihannsu behave like ancient Vulcans, if I am as bold to use our own history as a comparison-id say people dont change as much as we believe in a few thousand years.
In ancient Egypt, you had political corruption, religious customs based more on priesthood demands for power (sound familiar),and advanced technology for the time.
In Rome better records of the civilization allow us a better look at how that society worked-and again, political corruption, backroom deals, schemes for power by singular people, betrayal, economic and currency debasement, and in between were people just trying to survive.Oh, and advanced technology for the time.
Save for iPods and youtube, one could argue the man of today has the same motivations and ideals-and ambitions-as a Roman or Egyptian of what we consider ancient societies.
Id imagine its the same arrangement with Romulus and Vulcan society-while one was sourced from the history of another, the differences between the two are due to societal differences due to people in Romulus not being constricted by rule of law or logic, versus Vulcan.
I think of it like this-say you have a Vulcan man who has ambitions for running the planet.Within the context of Vulcan society, he has to either present a logical case for overthrowing the current elected government in favor of a dictatorship with him at the top, or he must channel his ambition into accomplishing enough within Vulcan society to generate enough of a popular base that he may logically propose legal election into power.
Given that choice, option B is a lot more promising than option A, which will probably lead to him being expelled or locked up, thus denying him the ability to take immediate gratification of power.
On Romulus, without logic as a barrier to personal gain, our Mr Ambition can scheme, lie , plot, murder, assasinate, and step on as many people as he sees fit to seek office of Praetor, as long as he simultaneously foils the attempt of competition to blow him away for their
own purposes.When you combine the opprotunity for advancement with the necessity of using morally repugnant tools to acquire power-and add in a Vulcan's natually powerfull emotional state-you have people of questionable morality leading an entire empire, and as such the greater will of that society will be severely inconsitent between regimes.
So it is no surprise that while Vulcan and Romulans could live on each other's worlds without being noticed, the societal differences are something like that of the United States compared to China.While a man in China and a man in America may seek high office like the example above-the consequences to that man differ from the society.An American president and likewise a Vulcan leader, need not be worried that a political failure or one moment of disgrace will result in an execution by a rival,unlike Romulus...or China, to a degree.