I am almost more shocked at your approach tbh.
I don't think it's a case of 'when the therapist signs off'.
I don't think there's any coming back from something like that. Forget 'rage' and all the descriptors that try so hard to kind of create the illusion that this is something 'happening to him' - when he gets better, he'll be the 'great father' he was before, right?
No.
There is, or should be, a very basic instinct to protect your child. If that isn't there, then I don't think it's something you can or should try and work around. He is not a parent. He does not have that instinct. He's a danger and he always will be, because he doesn't have that override. That override which would happily see him wallop his son, or push him - but hands round the neck and squeeze - NO.
He could very easily have killed him. It takes nothing.
And, 'good father'? Bullshit - what you mean by this is that he can do the 'playful happy dad' pantomime. They all can. When they're in the mood, the happy joking and the cuddles.
It's worse than being abusive all the time, because it teaches the child they can't trust. Dad is a wolf who puts on sheep's clothing, so be on your guard. Maybe everyone does it. Trust no-one. They don't really love you.
Your son is terrified of him and he will have been terrified of him all the time they've played and cuddled and your shit of a DH has been 'playing Dad'.
Don't ever call him a good father. If you can think he's a good father, you're not a good mother. And I'm sure you are a good mother.
You've taken the steps you need to take, keep him away permanently.