Here's the thing. To get a big score on the machine, you just need to keep the wheel spinning. You get no credit for how many times you thrash up and down the slide. So the trick is to get as long and powerful an acceleration phase as possible, and leave it spinning as fast as possible. Then you leave it, and leave it, and leave it, relaxing your muscles and letting the blood flow round them and coiling them back up again ready for the next acceleration phase.
There's detail in there. How you connect the drive through from your legs to your hands matters, so that you don't lose length from the power cycle. So does how quickly and smoothly you pick up the drive at the start, and how well you use the minor muscles in your shoulders and lats to get that last little bit, but the crux is there, in the long acceleration.
A half-good analogy is spinning a wheel on an upturned bike, with the flat of your hand. Lots of little taps won't make it go as quick as a few really long fast ones.
My back's knackered now so I'm not touching rowing, but last year I would do 10K at 21-22 spm, maybe rising to 24 at the end. I might do 2k nearer 28. I have history, so I would use a lower rate than a cyclist convert to indoor rowing, but YSWIM.
In a real boat there are other things that come into play. Not waving all that body mass around lets the shell ride smoothly over the surface, creates less wake and is generally more efficient. On the other hand the slowdown between strokes is much more non-linear, so you need to maintain a higher stroke rate to catch the boat before it's lost too much speed.
Rowers spend a lot of time rehearsing a perfect stroke at low SPM so that it will hold together and stay smooth at 40 spm, but concept 2 is simpler.