Cast and tempered aluminum has been used for many years and on millions of engines and tools (such as impact wrenches). Quality aluminum alloys are cast, tempered and machined. An hour of in-city driving is probably more stressful on an intake manifold, alternator casing, water pump housing, etc., than 10X or 100X hours of range use on an AR-type rifle. The AR design dampens its own recoil.
I realize there is considerable bias against cast lowers. But are forged-and-milled lowers really any better in a way that makes a difference?
If someone with metalurgical knowledge can answer this, or point to some real data, it would be worth knowing about.
Based on auto experience and observation, I think the bias against cast lowers is more a matter of snobbery than substance.