Assuming Romulans started with 10,000 colonists, what would their population be in 2000 years given modest 2% growth rate?
A generation being born every 30 years - in 2000 years, at 102% growth rate per generation, after 67 generations, their number would be 683400.
Bye bye romulans.
The scenarists' sense of scale isn't off only with regards to space, but sociology, as well.
Add a few centuries and every rag-tag band with a cool back-story is an empire.
Every conquered people can - and will - inevitably rise and free themselves, overthrowing their conqueror in due time (historic evidence indicating the opposite).
History is fluid - but not that fluid.