I would like to think that polishing the barrel and breaking in the barrel with moly coated bullets actually extended the barrel life a little. It seems to me that I get very little copper out of the barrels after shooting moly dry powder tumbling bullets. Mostly black. moly bullets are so slick that they lose velocity. you have to add a couple of grains of powder to run the same FPS as it's copper counter part
Moly does extend accurate barrel life -if managed. That management includes extended cleaning intervals with abrading it back to baseline. Otherwise, moly will reduce accuracy, and accurate barrel life overall, because it sticks to itself (wiping), causing constriction. That's it's disadvantage.
It does not reduce erosion nor velocity, because it's slippery. Moly in particular reduces heat/pressure as it vaporizes. Latent heat.
That's a benefit and what causes lowered velocities.
Moly, like most other coatings reduces copper fouling, as the loose copper doesn't stick to it well.
So for your goal of improving barrel life, with use of moly, I can see why you would conclude that polishing a bore is a good thing.
But for those of of us concerned about copper, polishing is bad and never good.
A better coating is tungsten disulfide (WS2). It is a universal fouling, that reduces copper, and cleans out well enough without use of abrasives.
While way slipperier than moly, WS2 does not affect velocities/pressure. It also does not affect accurate barrel life one way or the other.
It cuts copper fouling by ~1/2.
I dry pre-foul every gun barrel(long & short) I have with it, after cleaning. This, so my first shots are always on the money.
That's a big benefit for me.