The problem for me is Don
Kingsley did a fine job and everything but:
1 - he's just not intimidating. He's funny and off-putting, and socially inept, and completely bonkers, but he's not scary.
2 - a guy that out of control would never be trusted with any responsibility such as organizing a heist for the powers that be. He might be used as some kind of enforcer/hitman, but not to organize anything. He's way too unstable.
So I just didn't find his character believable. That everyone is so afraid of him might be explained because of his connections, but again, why would he have any when he's a raving loon?