I'll be honest...I'd blame the VET not the farrier. If that vet has been this horse's vet for over ten years he should have certainly seen the signs of chronic laminitis. People like to over glorify farriers...but honestly I don't go to a farrier for any kind of medical info...be it abscess, laminitis, etc. They have NO medical training whatsoever so I don't know why people treat them like they do. Of course I am an xray advocate...if my horse has any kind of limp I go get an xray and THEN show that xray to my farrier. Check the xray and see about rotation. From that point you can go on to shoe if needed or go barefoot. Alot of times foundered horses can grow more sole barefoot (with the use of hoof boots for cushion in the between stages). Couple of sites I've learned from when my horse had an acute laminitis bout.
EquineCushings : Equine Cushings and Insulin Resistance
ECHoof : EquineCushings & IR Hoof Photos & X-Rays
Pete Ramey hoof care heals founder in horse’s navicular disease farrier
Sounds like you've got the diet right. Make sure you don't forget about their mineral vitamin needs though. I use ADM Stay Strong. It does really well on my IR/Laminitis prone boy.
The Easyboot Glove | The Ultimate Horse Hoof Boot | EasyCare Inc.
Safergrass.org Articles on grass carbohydrates and laminitis
If I were to blame someone, it would be the friend that sold you the horse because they probably knew the issue existed and chose not to tell you or a vet.