Most perplexing thing about the application of red matter is it's ability to contain a supernova after it already has exploded, that is just bizarre. I mean I can accept that red matter can create singularities, that is ludicrous, but hey, so was Genesis device.
I can't understand why red matter would be any more ludicrous than, say, plutonium or electricity. Those are certainly pretty ludicrous as concepts, but we don't use that adjective for them any more.
As for the other thing...
Forget about the comic -
that's what's silly and implausible here. Only accept Spock's actual words from the movie. Let's try that one:
1) "A star will explode and threaten to destroy the galaxy"? Sure - if it was a star near Romulus. All hell could be expected to break loose if Romulus went. A literally true statement, even if we may have initial misconceptions about the nature of the destruction. And "galaxy" has always equalled "human-controlled parts of Milky Way" anyway; our heroes are not above looking at their own navels.
2) "A star went supernova, consuming everything in its path." Supernovas do that. If it were a neighboring star, Romulus might be in grave danger, and there might be only about a year or two of reaction time after the explosion. If it were the sun of Romulus, there would be no reaction time after the explosion (well, minutes, but nothing that would help). But let's note that nothing in Spock's words necessitates that the star blew first and the red matter mission was launched thereafter. The reverse order of events is also possible.
3) "I promised the Romulans that I would save their planet. We outfitted our fastest ship. Using red matter, I would create a black hole which would absorb the exploding star." This sounds like the Vulcans had just a few hours in which to act. This would be true if the explosion of the Romulan homesun had been predicted but had not yet happened. Red matter would have been projected to be effective against stars that are about to explode, although Spock would later be able to use it against a star that had already exploded.
4) "I was en route, when the unthinkable happened. The supernova destroyed Romulus." In other words, Spock may be saying that the supernova exploded, and that destroyed Romulus. So either the time of the explosion had been predicted wrong, or Spock was too slow. Both explanations work fine.
5) "I had little time. I had to extract the red matter and shoot it into the supernova." Romulus is already gone, yet Spock thinks he has time? Fascinating. Perhaps we do have to believe that the supernova explosion was threatening other stars, too, and not merely by destabilizing the Romulan Star Empire.
Or perhaps not. Spock seems to be saying that he didn't have any red matter yet, but had to "extract" it from somewhere after arriving. It seems the only place from which he could extract it would be the Romulan system. And indeed there'd indeed be little time to do that if Romulus herself was already gone; the rest of the system would soon be gone, too.
A third alternative is that red matter itself is dangerous, and that Spock would die if he didn't extract his onboard red matter in time and dump it. And dumping it in the supernova would be the only safe place, probably. But that doesn't jibe well with the fact that Spock survived just fine with a big lump of remaining red matter aboard his ship. Perhaps he just had to lose some mass to go subcritical?
6) "As I began my return trip, I was intercepted." The return trip would begin from the location of the supernova, since Spock dropped the red matter in the supernova, and the black hole was formed at the drop site - and the interception resulted in Spock falling into that black hole. Nothing in this precludes us from believing that the location of the supernova and the location of Romulus were one and the same.
So we don't have to believe in a truly galaxy-shattering explosion, merely in an explosion that would have results of some sort that would threaten the galaxy.
Now, the same dialogue could support the idea that the supernova was elsewhere, and destroyed Romulus in a faster-than-light action, and that Spock fought the supernova at its source, not at Romulus. But that is more difficult to accept, because shutting down the supernova at the source wouldn't save Romulus if the explosion had already happened.
Which of these two ideas is the less implausible in the end? "Distant FTL supernova" makes mockery of Spock's promise to save Romulus, and isn't physically completely plausible even with the usual Trek caveats. But "local realistic supernova" that threatens nobody else makes it unclear why Spock bothers with the red matter at all, after Romulus is already gone.
So why not go for a compromise? An explosion in the Romulan system is something that could happen on such a timescale that Spock would only learn en route that Romulus was gone. But that explosion could expand to neighboring systems at realistic STL speeds and threaten them, too - unless cut off at the source by creating a big black hole, a plan that might still be realistic a few minutes after the explosion. The mass of the supernova star would still be mostly at the center, and would make for a nice black hole. And if gravity moves instantaneously (as Trek often assumes), this black hole would help contain an expanding explosion cloud that moved at lightspeed - while if gravity moves at lightspeed, it would still help contain the STL elements of the expanding cloud.
Timo Saloniemi