To my way of thinking if a new holster needed "breaking in" then it must be a pretty crummy holster. Quality holsters are molded to the gun perfectly. They don't need "breaking in".
You are entitled to your opinion, . . .
Mine is that I as a leather craftsman CANNOT spend two or three days measuring and molding a piece of leather to perfectly match the contours of someone's buttocks, . . . hip, . . . waist, . . . belt line, . . . and extended or lack of love handles.
That is why I rely on a "breaking in" period, . . . where the owner / wearer puts it on, . . . wears it, . . . his body heat and the tension produced by the flexing of the holster on his body, . . . will make that perfect molding.
As far as the "gun" part is concerned, . . . even that need a break in, . . . as no mold that I have is a perfect match for the gun one of my customers owns. They will be close, . . . but not exact, . . . no matter how careful I am in selecting the mold.
I make my own holsters, naturally, . . . and I positively hate breaking in a new one, . . . but I know that when it's done, . . . I'll be more satisfied, . . . and I am, . . . MOST of the time. The other times, . . . wellllllllllllllllllllllll.
May God bless,
Dwight