You just described me.
I was 17 stone at around 12% body fat, destroyed my back during a weight training session and crept up to 21 stone in the space of a 2 year lay off. Always been big my whole life in a chunky way unless I commit a lot of time to training and nutrition to keep lean otherwise I get big quick.
My swing has changed so much as a result but i'm creeping back down now at 18 stone and feel quite comfortable.
I'm like John Daly one year then Brooks Koepka the next
My golf is more Arthur Daley!