In looking at the posted pictures, I see one glaring consistency. Many of those lowers were broken by someone using a wrench. I seriously doubt that the magwell would be split by any other means than using it as an anchor point for Bubba to apply mechanical leverage to some part.
Anything can be broken by someone with enough time, ingenuity(or lack thereof), and mechanical advantage-hence the phrase "break an anvil in a sandbox". If you send your aluminum lower, I can break it in any number of ways/points.
I have/had several PC lowers prior to the "mania". I don't use an AR as a prybar, club, or jack handle nor do I normally fall on my rifle. The average user will never encounter the need for these uses, either. Given the choice of having a complete AR using a PC lower and not having something I needed/wanted, I see no problem owning one.
My first choice for full on combat-probably not.
My best choice for a high volume HB varmint rifle-maybe not.
As an economical, available alternative in the current market-absolutely.