[barnstenchfartface]

The reason for the new Amazon seems pretty self evident to me, and well built-up as well. The shady guy from the company has explicitly expressed interest in commercializing the Amazon cells (and also the belt) for military purposes. This new Amazon is him doing exactly that.

Now, unless he goes out of control, he probably won't be an actual antagonist in the sense that he won't be actively working against the heroes. However, his existence is still definitely something both Riders would oppose, though for pretty much opposite reasons.

I don't think he'll be a "big bad," even if he does eventually become an antagonistic force that the others have to band together to fight. The real enemy in Amazons appears to be hubris, and this guy is just one more consequence of it.