That's true, in general, but, remember, everything's relative.

Given a 1500/2000 grit base plus a light to medium polish, a 1000/2000/4000 grit dull/matte finish will, in general, be slightly earlier, have slight less overall hook and have slightly less backend, while handling the same amount of oil.

The key phrase there is "in general". Because of the human factor, not everyone's "1500/2000 grit + light/medium  polish" will be the same. Nor will everyone's "1000/2000/4000 grit dull/matte) be the same.

I mean, I've seen people do a "1500 grit + polish" result in such a high gloss that I couldn't duplicate it in a month of Sundays with a 6000 grit white Trizact pad and a dose of Secret Sauce.

To return to sanity,
one can sand a ball to 500 grit, then apply polish by hand lightly to produce a finish close to a 2000 - 2500 grit dull/matte sanded finish.
Further, one can apply a polish by spinner to that same 500 grit and produce a finish close to 4000 - 5000 grit dull/matte.
(FYI There are 5000 grit Trizact pads that will leave a dull looking finish.)

Between polishes, compounds and abrasive pads, you can produce a world of variations, keeping in mind that
- the more speed dominant or matched (speed and revs) you are, the less difference these gradations will mean to you.
- the more rev dominant you are, the more use you can make from these variations or gradations.

I take charlest's amazing info from above as, YMMV.

Each person needs to develop their own methods they can duplicate and make adjustments from.  No two people will have the same result from a "1000" finish.  Different pressures, different ages of pads, time and with water or without.  I personally get away from the numbers in a descriptive state and do what is needed.  I know how I got to the surface I have on my ball.  If it is too late, I rough it up; too early and go up a grit.  Doesn't matter what the number is since it won't be the same as anyone else.

One thing to note from above is the differences in skipping grits as to using all grits up to your final pad.  Also, differences in adding polish with varying underlying grits.  I personally don't use a lot of polish, but if you do, be careful how you apply it. 

For me also, when experimenting with surfaces, I like to take a higher grit to the center and reduce the grit as needed by hand.  Much harder to go higher without the spinner.  May be harder to duplicate, but I have had too many instances where I go with my version of 1000 and in honesty needed 4000 or so.

Awesome, appreciate the info!

So say I want to get a little more backend out of my 3000 sheen oob Rocketship. What would be the next step you would take? Don't know that I'm really changing it up but as an example to help me better understand.

This sounds familiar?
More backend - 4000 grit on top of the 3000. It will go a little longer and have a little more backend because the extra length saves just a little bit more energy. (There are 5000 grit pads, as mentioned above for more of each.) It's not a drastic changes, but if you're rev dominant, you'll see some. If you're speed dominant, you may need a total change - something like 500 grit sanding + a light polish, but this is is a little more complex to implement, and may need some experimenting.

Quick question on touching up a "skip a grit" surface finish, say 500-4000 as an example.  Would you repeat the 500-4000 steps, or just hit it with the 4000 again?

Fyi, when I initially do this surface, I do 500 on 4 sides, 20 seconds each at medium pressure, then 4000 on 2 sides, 10 seconds each at very light pressure.