One thing that sets up rotors and especially drums up for issues is how they are stored at the store/warehouse. They need to be stored flat, not vertical. Most places store vertical as it eats up less space. How long were they sitting like that? When I worked at a NAPA store in the early 90's we stored them flat and had no warp issues. This was after finding out we had more returns due to warpage from being vertical. Add the prevalence of overseas manufactured units, like now, with questionable machining and you have your current results of issues. Maybe buy better made units? Hard to say. Even major brands get stuff done offshore. For sure though, once you cut them to true them up, you lose material that would have been there to help absorb the friction heat thereby making it much easier to warp the units when you are on the binders hard or for a long period.