It still makes for a pretty damned backhanded compliment.
Understandable that it came off that way, genuinely not intended as that.
It's bloody hard to express something sincerely on the internet without sounding like you're just being sarcastic.
IMO the best way to go about it in this case would have been simply to express your appreciation/admiration/whatever for his actions here, and ignore the past. That would clearly imply that you've at least somewhat adjusted your opinion, without having to explicitly bring it up.
Of course, it also wouldn't have spawned a hundred-comment sub-thread.
Why? I'd rather have someone tell me what they thought of me and that I managed to change their mind.
I can understand that POV, but I expect you're in the minority. Most people in my experience respond better to "I respect you," than to "I used to think you were a cock, but now I'm reconsidering and starting to respect you."