If a manufacturer wants break in, I'll follow it....sort of. If I buy a premium barrel from someone like Obermeyer, Krieger, Schneider, etc, they make the inside of their barrels exactly like they want them to be.
It would be the height of arrogance for me to think I could do anything to improve on a barrel made by someone like Boots Obermeyer, by going through some break in process I came up with.
Manufacturers don't need to do any empirical testing to see if break in is a myth or useful. Doing really scientific testing would be very expensive and the manufacturers simply don't need to prove anything to anyone, so truly empirical, scientific testing to see whether break in helps or not simply isn't done. Break in does help wear out barrels faster because of the extra ammo run through the barrel. And that means consumers might have to buy another barrel sooner.
While I am unlikely to do break in, I don't mind if anyone else wants to go through some process. I do think that proper lapping of a barrel may smooth out some machine marks.