I agree. Maybe there is some theory to this, but I ride untrue rims on beater bikes all the time and can confirm this has no effect on wearing the braking surface (except at the points that bulge out.)

What matters is using good quality brake pads and keeping the metal shards out of them. Crap brake pads will grind down any rim. mrrabit's comment on the cheap CNC'd rims is also accurate. I've seen it happen on cheap rims.