Great news that he has made such a turn around for you!
My gelding Claymore was also gelded at 6, right before my purchase of him, and was used as a breeding stallion up until that point. He was primarily pasture bred so didn't lack the social skills and was respectful of mares, thankfully. But I did have some issues with him being very hard and non responsive initially. A book of exercises I found very helpful with him was this one: Amazon
.com: Lessons in Lightness: The Art of..."> Amazon.com: Lessons in Lightness: The Art of...
I'm now 2 years in with Claymore, and can comfortably put beginners on him. He will always be a dominant-natured horse I have to be firm with, but as long as I keep on top of him he is very reliable. He does act somewhat aggressive with other geldings in the pasture, but only to a point of asserting his dominance, once they back down he doesn't bother them.
I think when you are talking about a horse that was not only gelded late, but was actively used for breeding, there is more involved than just waiting for the hormones to clear the system. It takes a while, but you can get there. I would say from the video it certainly looks like he has come a long ways and will turn into a nice gelding.