Why do you think he's the secondary antagonist? he was more evil than Ghost and his plans were more evil, Ghost wasn’t really evil, she just wanted to cure her own condition so Sonny had bigger plans so Sonny Burch is actually the main antagonist, the actors name appears first in the credits, hinting this. I even wrote in the summary.
Being "more evil" and his plans being "more evil" isn't enough, the story just doesn't focus on him much and it's clearly Ghost who's presented as the main that. The actors name thing is irrelevant as well, that has nothing to do with the antagonist scale
Threat I meant and he doesn't have bigger plans, all he wanted to do was steal Pym's technology. That's not any bigger than ghost in spite of her sympathetic goals and again she's the one who's focused on. Birch is just a random criminal
But Sonny Burch wanted to make money by selling Pym's technology to potentially dangerous bidders and taking out anyone in his way with no remorse, whereas Ghost merely wanted Pym's technology to cure her own condition. he seems to have bigger plans to me, is it because he never gets the technology to do what he wanted to do?
That's not exactly bigger plans in the context of the movie, and I'd say yes since we never see anyone trying to buy them or him succeeding in selling. Ghost may have wanted it for sympathetic reasons but that doesn't give her a get out of jail free card, her plans were just a big and she was a more immediate and dangerous threat while Burch seems quickly forgotten about