The "farthest reaches of space" thing has never been a major part of the Romulan identity in any case. Our heroes always easily reach the Romulan territory, even if they have some trouble communicating with home base; it's probably more an issue of bad relay networks than distance.
I don't concur. Let's take a look at "Balance of Terror" first.
Captain's Log, stardate 1709.2. Patrolling outposts guarding the neutral zone between planets Romulus and Remus and the rest of the galaxy, received emergency call from outpost 4.
What's the rest of the galaxy? Either the Romulan Star Empire sits at the edge of the galaxy or at its center.
At this distance a reply from Starfleet would take three hours and possibly the producers realized that this isn't necessarily a big indicator of distance. Fast forward to "The Enterprise Incident" and you definitely have some distance to write home about
KIRK: You understand that Starfleet Command has been advised of the situation?
TAL [on viewscreen]: The subspace message will take three weeks to reach Starfleet. The decision is yours, Captain. One hour.
Compared to "Balance of Terror" this is either a changed premise or tells us that the Romulan Star Empire sits in the center of our galaxy (to rationalize descriptions like "rest of the galaxy [surrounding this center]") and events in "The Enterprise Incident" take place on the far side of the Neutral Zone.
(if TNG altered this TOS concept than it's just a case of retcon activity and possibly lackluster research)
why did the exodus Vulcans voluntarily deprive themselves of warp drive technology so that a few thousand years later all they have is "simple impulse drive"
This has always seemed to me like a huge leap of illogic. Nowhere in "Balance of Terror" does any character suggest that Romulans as a culture would lack warp drive, even if the single vessel encountered is deemed to lack it.
Appearances can be deceiving and in this particular case I believe it's due to a lack of three-dimensional thinking and imagination (no offense, you do know that usually I admire your unorthodox and extensive examinations).
KIRK: Yes, well gentlemen, the question still remains. Can we engage them with a reasonable possibility of victory?
SCOTT: No question. Their power is simple impulse.
KIRK: Meaning we can outrun them?
STILES: To be used in chasing them or retreating, sir?
KIRK: Go ahead, Mister Styles. I called this session for opinions.
I don't see how this can be interpreted in any other way than explicitly stated by chief engineer Scott.
Yes, it's probably a long travel at sublight speed from Romulus through the Neutral Zone but we have no information whatsoever when the Romulan ship departed and when it was expected back, add to this we have Romulans that do share the long life span of Vulcans.
And if the ship would have had warp drive and be back for dinner on Romulus, there would have been no need for Decius to break the rule of silence, send a message to the homeworld and thus endanger this Romulan mission.
And for a ship passing through the tail of a comet to become momentarily visible to become a target rather suggests sublight than warp speed; doesn't it?
It is also blatant in the episode that Romulan weapons travel at high warp, so any character speculating on the lack of Romulan warp technology would be wildly off base.
The only episodes where it is obvious that the Romulans (then) do have acquired warp drive are "The Deadly Years" and "The Enterprise Incident".
You are arriving at your conclusion based entirely on a two-dimensional map (apparently a simplified graphic for the ship's crew to apprehend the situation) which lacks three-dimensionality.
For all we know the Enterprise
is literally nose-diving or sky-rocketing at warp speed towards the position of the Earth outposts in actual space, for all we know we are just looking at the top of the Neutral Zone "Wall", diagonal passage through which will eventually bring us to the level of the two objects to the right side of which one is apparently the planet Romulus and possibly not its star but just its moon "Romii" or "Rom II"