I've done testing and have seen test's in comparison of barrel's broken in according to manufacturers recommendations and a total disregard of those recommendations.
It all came down to how well the barrel was made, what material it was made of and what type of projectile you were shooting.
Some barrels from the same lot of steel wear in quicker and clean better than others, so it's just the luck of the draw sometimes.
I've taken rifles fresh from the factory, made sure the bore was clear and shot it till the rifle wouldn't chamber a round.
The other rifle was broken in with the shoot, clean, shoot, clean break in process and it didn't make a difference in accuracy between the two.
We also lubed and cleaned the broken in barreled rifle.
Both rifles were tested strapped to a lead sled, so no shooter error would be introduced into the equation.
Hundreds of rounds with only a borescope inspection to see if the barrels were getting compromised with copper or carbon buildup.
The two test subject rifles performed the same in accuracy and barrel fouling testing, but without proper cleaning of the chamber the un broken in rifle crapped the bed and wouldn't chamber or extract a round without using a mallet on the bolt.
I leave barrel break in to the person buying the barrel.
SJC