Cameron's lore is boring and turns the xenomorphs into space bugs.
He didn't COMPLETELY pussify them. The Aliens from
Alien didn't have some impenetrable armor covering their entire body, it was just that no one on the Nostromo had any guns. The Aliens from
Aliens weren't all of a sudden made of glass, but those auto-turrets still turned hundreds of them to chum. Cameron didn't "turn them into" sniveling insects, he just jacked up the scale of the confrontation.
People may find that unfortunate, since a single Alien was such a formidable enemy in the first film. BUT what Cameron wanted to make was a war movie, and I think the Alien itself stayed true to it's ferocity in Scott's film. They just happened to encounter .50 caliber bullets.