Apples and oranges. Your back is fully supported on a recumbent.
I don't think I have ever heard of someone's pelvis or spine being permanently deformed by a seat (of any type) they sit on.
Core work, stretching, etc. is a virtue, regardless of what kind of bike your ride, and what shape the seats are you sit on. Riding a bike is riding a bike. It's not exercise for your back. Exercise your back using back exercises.