Yeah, we always wonder what he had to deal with. He's still very sensitive to any pressure at all on his ribs, and he hoards soft toys in a den (under a bed), though he responds with exasperation rather than anger if one is taken. When we first got him, he tried eating acorns (hell on a dog's stomach, I understand), pre-emptively winced the first time he barked in view of me, and despite generally hating to go outside any longer than it took to potty, climbed up on our patio furniture to investigate the fence the first time we had to leave him with a sitter.
These days, he's fat, which is a negative of course, and he's still an idiosyncratic homebody, but he's also confident enough to ask for affection, isn't reactive to anything other than vacuums, and has a great relationship with our other dog. The turnaround has been lovely, and if being a chonk came as part of it, I think it's a trade worth having made. Our other rescue was born after his mother arrived at the foster, and has a very different relationship with food, exercise, and new people. His super playful but emotionally aware energy has worked well with our "seen some shit" heeler.