What you say is true Uncle...that's what I was hinting at with the "sliced bread" comment without going into any details. Most shooters will buy a "firelapping Kit", follow the steps and have NO IDEA the "what's and why's" going on in the background. If it DOES work, it's great...if not...well maybe you've read some of the exceedingly hot flames produced by "failures" on many forums.
BUT, the merchandise being sold is that a smoother barrel will shoot more accurately AND be easier to clean...and as far as a factory hunting barrel, that's about all you can ask for. AND it does work fairly well even on 100 year old military barrels. Hardly anyone even knows OR cares about the nuances that are happening, they just want the illusion.
I quit doing lead lap lapping way back when, much preferring to use a fairly snug cottom mop or patches wrapped around a jag and fine valve grinding compound to get the worst of the bark nocked off, then the pleasure of shooting took care of the rest...I never thought to use grit on a bullet and actually fire it down my barrels...you know the mantra of "clean ammo"...
John Barsness did a very interesting article on barrel lapping in the Nov, 2001, #198 RIFLE magazine that might be of some help to those thinking of barrel lapping.
The thing about it is the fact of "NON-UNIFORMITY" in all aspects of firelapping...I've read to lap at low velocities at one place...higher velocities around 2000fs at another, use ANY old cast lead bullet, use ANY bullet period, and TUBBS NECO sells their kits for use with lead, jacketed AND also coated JACKETED bullets...pretty good merchandizing and a way to turn a couple thousand percent profit(or more) on silicon carbide grits and bullets, at least until everyone else jumps in and screws up the market.
I just bought 4 oz of 320 grit paste from Brownells, ~$18, for firelapping a 444S barrel and used a gob the size of a pea to do 10 - 265 gr hard cast bullets and that left enough on the steel flat bars to do at least another 25 or more.
I bought a jug of 600 grit about 30 odd years ago I've been using to POLISH many of my barrels, bolts, raceways, small parts etc and also used the stock polish Brownells sold back then...they all worked to a greater or lesser extent...at least in my mind.
The people who sell hand lapped barrels have their own procedures and those that use a lead lap follow well established fairly old procedures, but otherwise it's...who knows what.
Maybe the fact that firelapping within the specified parameters DOESN'T ruin many barrels and actually does some good, keeps the lawyers away.
LUCK