Actually, it's about opinions. Show me scientific data that backs up the notion that breaking in the barrel is bad and make me a believer. Links that are someone's point of view or opinion don't count.
If breaking in a barrel is a myth, why do bench rest shooters do it?
People do all sorts of thing because it's been told to them or it's out of habit. It doesn't mean it's correct.
Do we really want to list off all the weird stuff that competitors in sports do because they think it makes a difference?