help dragons skin is coming off not a shed

I have a rescued dragon I got almost 2 weeks ago its in bad shape I got it its getting a little fatter but not much. the person said its over 2 years old and her son had it but didn't take care of it she got it out of his apt after he got put in jail. The skin is coming off at elbows, knees, and hip and front legs where it moves a lot and its white under it, its not a normal shed I know that. his spikes are very soft and not hard like my other dragon. I been giving kale, collard greens and spring mix and taking spinach out. And every other day dubia roaches with calcium d3 powder. There was a few times he threw it up after a hour or so, He's very dark and bad looking I feel bad for him. I spray him once a day and his basking areas at 95-97 and cool side is 78-80 and uva/uvb light, I do a 12 hour cycle and night time temps are around 75 I have a top of the line raytek temp gun to check temps on all my reptiles. Is his skin too dry or is it from poor care from other owner? I want to make him as happy as can be when I first got him they had him in a 20 h tank and barley moving and he will only eat smaller roaches too. They only fed him dried crickets and mealworm and greens a few times a month. What can I do to prevent his skin from falling off? Thanks