Enterprise showed the Romulans had warp drive, and in Insurrection Admiral Doughtery said something about warp drive turning a bunch of Romulan thugs into an empire. in that case, I would apply that line from TOS to mean that specific ship only, not to the every single Romulan shpi, especially one from 100 years prior.
There's just very little information from on screen sources about what happened during the Earth-Romulan War. The dates I got came from the novels because that's all there is, but novels are not canon. It's really a wide open playground for an author. I would not take those dates literally at all.
I think the Earth-Romulan War would be more believable and fit into canon if the majority of the conflict took place in the Bassen Rift.
- It would explain the lack of visual communication between ships, since the Bassen Rift does not allow for long range communication due to electromagnetic distortion from the gas clouds present. Since even the Ent-E was unable to request reinforcement when under attack by the Scimitar in NEM, and they had far more advanced tech than in Archer's time.
- Its believable that Romulans would commit raids on Earth colonies and freighter routes with Warbirds, leave a tracable trail for UE forces to follow them through boridium, only for Earth forces to be ambushed by BoPs and other Romulan forces in the Bassen Rift in the style seen in TOS
- It would then give a reason for more primitive Earth ships to be involved. It was established in ENT that freighter ships under the Earth Cargo Authority were not allowed to hold prisoners. So they were likely participants in the conflict, since it fits with the explanation that the conflicts allowed for no quarter or capture.
- Plays it up as a defensive war from the Romulan perspective, and keep the canon from TNG that Romulans rarely initiating conflict first, preferring to test resolve
- The Attack on Earth in spring 2159 while Archer and co. are vacationing on Risa (from ST: the Beginning) is when the Romulans oversteps their bounds
Basically, it would make the Earth-Romulan War be the WWI to the Dominion War’s WW2.
It also would not prevent the following battles from occurring:
Attack of Station Salem One aka Starbase One (preamble to war)
Battle of Algeron (first battle of the war)
Chulak of Romulus being defeated at the Battle of Galorndon Core (referenced in VOY: The Thaw)
Battle of Vorkado in 2159 (referenced in VOY: Workforce, part 2)
Battle of Cheron, Coalsack Nebula (final battle)
It would then be a matter of establishing how the Coalition of Planets fell apart between the end of Terra Prime in January 2155 and before the founding of the Federation in 2161. What the terms of surrender were for the Romulans (UE gives them warp drive to expand their empire in exchange for a Neutral Zone?). Then, whether or not Captain Edisons's resentment of the integration of MACO into Starfleet after the war was widespread after serving in the Romulan War. And why the Vulcan philosophy of a Prime Directive wasn't adopted until 2167.