For that matter, why travel in the line of the Big Plasma Ball of Death's direction instead of perpendicular to it?
Who says they ran in a straight line? The TOS-R version makes it amply clear that the cloud of death can steer (they show it doing a nice swoop from below right after launch, primarily so that the cloud won't obscure the cool Romulan ship). Heck, for all we know, Sulu turned the ship completely around so that he could flee bow first. He just didn't want to turn the camera away from the one and only target of interest.
On the map issue: it never occurred to me, when watching as an isolated fan, that the map showed only a single star system. After all, the map itself identifies as name-worthy locations Romulus and Romii. I can't get behind Romii as an alternate designation for Remus; the kerning just doesn't work.
The ring around the dot dubbed ROMULUS may be taken for Remus, regardless of artist intention. But we know something about artist intent in Trek: every time a "star system" is explicitly portrayed on screen in TOS (from "The Cage" to "Spock's Brain"), we get nice concentric elliptical lines on which the planets or assorted other objects are riding around the local sun. This one is not in the tradition of TOS star system maps, then.
We get draw some conclusions about the distance between Earth outposts from the transcript: Outpost Two goes silent an hour before Outpost Three, so unless there's multiple Romulan birds-of-prey in action it took under an hour to get from one to the other. Also the Romulan ship manages to get to outpost Eight, giving outposts Four through Seven a pass for some reason.
The multi-ship attack theory would not just preempt possible contradictory evidence, it would be nicely in keeping with the submarine analogy. And no doubt a synchronized attack would have been attempted by the Praetor - but in true submarine style, stealth would ruin the timing, and some of the boats would fail to reach their targets altogether.
Another way to view the chain of losses is to assume that the Outposts also maintain stealth. "Going silent" does not refer to sudden cessation of transmissions, then, but to a scheduled communications burst failing to be sent. This, too, would rather completely negate the value of the evidence - for all we know, Outpost Seven was the first to fall, and the heroes just don't know it yet.
But there's no making sense of any estimates of Original Series sensor ranges.
And the Outposts could be among the most challenging targets, designed to be stealthy against starship sensors. One might have to get up close and personal to observe the cloud of inert rubble before being able to tell whether the Outpost is Out. Supposedly, such observations would involve insystem ranges, as per "Doomsday Machine", although our heroes here could jump to conclusions on lesser evidence.
Enterprise is able to get debris from Outpost Four while still an hour outside the Neutral Zone. The Enterprise is matching the Romulans' speed at that point. So this would seem to be a key to working out speed capabilities.
The heroes were only five minutes away from Outpost Four when the Romulans destroyed it in a sequence that can be argued to take five minutes. So when Kirk orders "parallel course" at the conclusion of the carnage, it's quite possible the ship has already reached the Outpost coordinates and Bailey has stopped here there until Kirk makes up his mind. Sampling of the shattered armor could have been conducted at point blank range, autonomously by Scotty, who would only spring the news at that "one hour from RNZ" timepoint.
Again, this would mean (welcome?) loss of evidence value. As for Scotty's odd antics, well, he
would be doing something unexpected on his own initiative, and would not be expected to report immediately, not when Kirk had more pressing matters to attend to. OTOH, what Scotty did would require minimal effort - after all, we never hear Kirk ordering shields raised, and while we can assume those did go up at some point of the episode, they need not have been up at Outpost Four and blocking the transporter. Scanning was paramount at the time, after all, and keeping shields down might be the recommended procedure.
Eight (at least) Outposts seems excessive to me for one star system
The layout of the map, potentially showing one quarter of a circular RNZ, suggests that enveloping a sphere consisting of four such mapfuls in one plane would take two dozen Outposts at least...
although I suppose we only have evidence that one held any crew.
Certainly #4 was atypical in it taking two shots to achieve a kill, or whatever the factor that allowed for a message to be sent out. We could just as well add to the atypicality and say that the extra armor was because of the crew.
I'm already on record as being fond of the faster-than-light impulse interpretation of things. It makes sense of Kirk asking whether the Romulans having simple impulse means the Enterprise can outrun them. It also makes sense out of the Romulans challenging an Earth that they would seem to have to know has faster-than-light ships. Not that speed is everything, but I wouldn't want to take on an opponent with an advantage that vast.
Romulans could always challenge Earth with ships that have high warp - this would mean nothing to their considerations on whether to challenge Earth outposts with ships that are sublight only. Submarine warfare (or, say, infantry warfare) doesn't necessarily imply unavailability of intercontinental bomber aircraft or ICBMs, after all.
Let's remember that our heroes are analyzing a single vessel whose attributes (invisibility, weaponry) have taken them by surprise. They can't be throwing around conventional wisdom about generic Romulan ships, least of all CW a century out of date, when arguing that their power is simple impulse, then: the accusation must be specific to this one vessel. Whether correct or incorrect, it ultimately fails to tell us anything about the weapons of the old Romulan War.
Timo Saloniemi