I haven't watched the clip, but there's nothing to review. He beat the best guys available during his prime. The division got hot as he was exiting his prime.
I agree that as the level of competition rises, KOs become rarer and that Golovkin was already older when he got to those fights. He could have try to move up while still at his peak though. 160 was one of the if not the weakest divisions for some years. I remember top names other than GGG around that time consisted the likes of Geale, Murray, Quillin, Lemieux, N'dam and the likes...
These are not bad fighters but neither of them is on the level of let's say a Jacobs.
The only other elite guy could have been Martinez but that was just the wreck of Martinez already.
GGG could have moved up in weight and challenge someone for a 168 title but he didn't, he decided to stuck in 160 for years, either because he didn't want part of 168ers or because he was already waiting for a Canelo fight to come up even though they were years from Canelo appearing there or maybe for some other reason but he never did so he can blame himself mostly for not getting any of the top fighters while he was at his absolute peak. He decided to never move up...
With that said he's still a surefire HOF-er, he dominated good opposition for years and beat some very good fighters too like Derev or Jacobs even though not clearly. The Canelo fights were both very close and regardless that I had Canelo winning the rematch Golovkin proved he belongs to that level in these fight and that he wasn't just a hypejob.
So the coin has 2 sides, on the one hand he is a HOF-er and was as elite fighter in his prime, on the other hand though he never dared to be great and this way he's a bit of a wasted potential too.