For a long time, I've thought this line by Spock in 'TWoK' referring to the Reliant overwhelming the Enterprise spoke almost exclusively to the fact that the Enterprise was heavily damaged.
However, if you think about it, a Miranda class vessel might indeed be faster and better armed than a Constitution on an even playing field.
The Miranda's mass would appear to be considerably lower yet she at least outwardly possesses largely the same engine equipment. One might argue that her powerplant could have been less potent, but then again she also appears to have two deflection crystals to the Connie's one, so the contrary might be arguable.
Miranda also has two forward torpedo tubes and two aft torpedo tubes to Enterprise's visible two forward tubes, as well as the two rollbar phaser cannons which some call 'megaphasers' but for all we know don't pack that much of a punch. Miranda does, however, omit the ventral and above-shuttlebay single phasers that the Connie is equipped with.
Further complicating the matter, perhaps, is that in Kirk's surprise prefix number attack earlier in the film, he seemed to score a pretty good hit near one of those deflection crystals, possible somewhat equalizing the situation? Saavik's and Spock's lines indicating that 'visual won't function, and shields will be useless' making the odds even are interesting too. Would a lack of targeting and shields really render the damaged Enterprise an even match for Reliant?
I would argue that this may indeed mean Reliant was damaged comparably to Enterprise, if not as severely,and that all of this when taken as a whole indicates that the Miranda class might indeed outrun and outgun a Constitution under nominal circumstances.
What say you?
I think that the "Miranda" (nee "Avenger") design was less capable, overall, then the Constitution-refit (nee "Enterprise") class design. But "less capable overall" doesn't mean "less capable in all areas."
The Heavy Cruiser was designed to be the "jack of all trades" ship... a science vessel, a cargo carrier, an explorer, a warship, a travelling diplomatic mission. And it was very good at all of the above. But, inevitably, a ship specifically designed to serve in a particular function will always be more effective at that particular role than any "jack of all trades" design possibly could.
The Reliant was really designed primarily as a warship, it seems. Shorter range, far less cargo capacity, no big honking "main deflector." Probably less power output, overall, but less tonnage to carry around as well, so potentially a slight edge in "power output versus power consumption."
The trick with the Reliant is that it had basic sensors, but no specialized sensors like you'd expect on a science vessel (like the underslung pod carried by the Grissom). So why use it for the role it was performing in TWOK?
Simple... the Federation Counsel knew how dangerous "Genesis" could be, so they assigned a powerful warship to support the job.
As for "outgunning," that's obvious... the Reliant had the same number of Primary-hull dual emplacements, lost the handful of single-turret emplacements on the secondary hull but replaced them with direct, in-line-with-main-power heavy phaser cannon, and added an additional aft-firing torpedo. More weapons, overall, and potentially heavier ones to boot (The location and configuration of the torpedo pod on the Reliant has always inferred, to me at least, that it might have been firing heavier torpedos than Enterprise was, too.)
As for outrunning... the total mass of the Reliant was significantly less than that of the Enterprise (based upon assumptions of constant density - note that the ship has lower volume)... and the impulse engines were significantly larger. (Anyone who's ever built a Reliant model knows this.) So, at sublight, it makes a ton of sense that the Reliant could outrun the Enterprise. For the two reasons above, it would be able to accelerate much faster - which is what we see in the film, of course.
Now, as for WARP speed... I'd be surprised if the Enterprise couldn't have run circles around Reliant. And for range... the Reliant would have to turn around for resupplying long before the Enterprise would have to consider it, most likely.
This is why I refuse to accept the Reliant as a "Cruiser" (or "light cruiser") but rather think it's a Frigate. It's best suited to serve the role of a frigate, in modern naval terms.
So why use that, instead of a cruiser or a science vessel, to support Genesis?
Well, the cruisers are the "Glory hogs" of the fleet. When the Enterprise, or the Farragut for that matter, get deployed someplace... people pay attention. But send a frigate someplace, and it's pretty well ignored, most likely.
Genesis required security... and that security was supposed to stay relatively nearby (close enough to be on-call if any bad guys showed up). So a short-range(ish) ship with lots of weapons would be ideal on that basis.
And, of course, all we saw Reliant doing was identifying "likely targets"... not doing the final, in-depth surveying that would likely have occurred. Consider how poor Reliant's sensors really were... barely registering anything on their scans, when in fact there was a large group of people. The Enterprise has been able, in the past, to identify a single person with no trouble. And Grissom, in the same situation, would likely have been able to tell what Khan had for breakfast the day before.
I wonder... was Grissom also assigned to Genesis already, but just wasn't on-station at Regula? They DID say that "everyone was on-leave"... maybe they'd gone on-leave by being ferried someplace by Grissom?