Statistically, weight is indeed a risk factor for bumblefoot ! But my experience is atypical.
That's an interesting experience, I definitely have some birds who seem more prone to bumblefoot and because they're on the bigger side I guess I assumed that was the reason; correlation =/= causation I guess. Don't know how most of mine were bred, some are hatchery(Hoover's, I won't be buying from them again for a few reasons), some i got from other backyard people.
I am hoping I can breed away from the ones prone to it, though, with time. Pointy stuff in the soil definitely sounds like a culprit for at least some cuts n scratches.
Our soil is more clay-based here, of course that means it is mud season now and I am fighting a losing battle in the chicken area over that, but less pointy stuff I guess.
I lowered the roosts like you a bit, have added ramps to come up and down, and sanded all the roosts, and that did not solve the issue. I think it comes from our rocky harsh soil and the fact that our chickens range on old farm land and keep digging up tiny pieces of trash and rusty metal. I also believe it's possible that the chickens who grew up here as chicks had their feet's cushioning become more adapted to rough conditions. That's why I'm thinking of trying to reproduce that ; but I will wait until the dermatitis are healed.
I do have one other bird with some mild bumbles right now, and I've been doing semi-regular baths for him when I've got the time and babying the heck out of him. He's on the bigger side, but his parents both had issues too (One is Goose

). I really won't ever shake the fear of hurting them via trying to help, I don't think.
I've heard anesthesia can be hard on birds for sure, that and pain meds. It's got its risks for people too, but worse with birds. We don't have any kind of vet around here that could help with chickens, hence having to make do with what we've got at home.
Anyway on Goose updates:
He is hopping around more these days, seems to have his energy back and with a live-in girlfriend (One of our hatchery brahmas) he's quite happy, I think. I'm going to have to get him/make him a chicken wheelchair or something ASAP while we wait on his leg to finish healing for the prosthetic stuff.
But wound is looking good re last bandage change and his energy is pretty much back to normal. I'll have to see if I can get a picture next time I do the changes but there's new flesh and it seems to be closing up fairly quick overall. I wonder what the rough timeline will look like once it does close, that is, I imagine there's still a lot of healing the internal parts need to do.