The movies about the end of Spaces cold war, not fighting a bad guy.
The rest of the movie is political manuvering and a jail break, of which we hardly see Chang in. TUC has the conspiracy, a Co - ordinated group of extremist political opponents of which Chang is the face to Kirk and Co, but he's not really key until the final fight. And then fight a growly bearded special effect for ten minutes. TFF has Sybok as a villian in the beginning but even Kirk, who is not under his spell, sides with him in the end and they adventure together looking for God. Like TMP it isn't a villian, but another "force of nature". It's at the very start of the movie and the very end. TVH has a probe looking for whales, not trying to destroy Earth. He's not the driving force behind the movie, he is the B plot. TSF has Kruge, but the Enterprise crew doesn't even meet him until an hour into the movie and he's easily dispatched by Kirk with a boot in the face. TWOK is the most villian driven TOS film, but the villian and the hero never even meet face to face - it's more about the themes of ageing, loss, revenge. The "danger" is incidental, like a force of nature, not directed. Which it does, in an ultimately peaceful and mutually agreed upon way. TMP the "villian" was a giant space probe come to meet and join with its creater. The thing is, the Trek movies prior to FC were never about the villian. I like Bana, but Nero, as presented in the film, is pretty 2 dimensional.