I think my undereducated grandmother subscribed to the “wholesome” thing because she thought raw-ish foods might not have all the germs killed yet. On the other hand, my *other *grandmother got a bachelor’s degree in Home Ec, and she never overcooked vegetables.
Also, safe home canning procedures can lend themselves to overcooking: high temperatures while canning are needed to make the seals tight, and if you have a lot of stuff to can, or aren’t fast, the end of the batch might get pretty soggy.