Regarding the artificial quantum singularity power source, complexity doesn't necessarily imply superiority - quite the opposite might be the case.
If you create fuel for your cars with the Fischer-Tropsch method, that's "advanced" and "complex" but establishes your nation as a pariah state lacking in natural resources. If you use wood gasifiers, you're toying with even more complex technologies (and risking your life every time you take a ride), but that's because you don't have oil wells.
Romulus might have been forced to develop AQS systems early on because the peace treaty left it with a fixed territory devoid of natural dilithium resources. Indeed, perhaps there never were any dilithium-powered starships in the Romulan Star Empire, and that's why Scotty was fooled into thinking that the Romulan plasma mortar vessel would lack warp capacity altogether (when all it had was an inferior if advanced and difficult-to-identify powerplant).