TBH, I don't think the injury has had all that much to do with it.
Was watching him bowl vs Australia in early 2000, in New Zealand, and even though he took a heap of poles (12 for the match, I think) his front arm did nothing, he was a lot lazier through the crease. He'd have the odd good series, and then go badly after that. However, now he's a lot taller at delivery point, his front arm is really high and pulls him through. He's got a very easy, repeatable action - something which wasn't there beforehand, leading (IMO) to a lot of his troubles.