Gaolang practiced in muay thai for whole 20 years, switched to boxing and mastered that too. He's arguably the best boxer and nak muay combined in kengan universe, you can't really downplay that as someone "just using boxing and muay thai."
Fang was probably weaker than Gaolang's full power at the start of this match, but Fang's "evolving" as the match goes. You need to defeat him before that, but Gaolang still hasn't managed to score that deciding hit, and we all know where this will go.