The insectoid features were first referenced by the Alien team. Cameron just knew about that and expanded on it a bit. It was the comic writers licking Cameron's balls that took it over the edge.
And considering that Scar fires a lot of blasts and kills about three or four Aliens, I'd say that dodging those plasma blasts wasn't too difficult. Especially since they know what's coming. To compound our point, one Alien was dodging bullets in Alien: Resurrection. At close range.
I mean, c'mon, dude. The plasma caster obviously blows them to bits really effectively, but there's nothing saying that it's a surefire hit in the first place. It's not like human beings have never evaded it, and Aliens are far more agile. A Predator just can't look at an Alien from long range and go "kerbang, you're dead". The shot has to be well-considered and well-timed. That's not always possible.
The whole scenario of one Predator taking down multiple Aliens with ease on a regular basis is a f**kup by hack writers who just wanted to have the next Aliens on their hands without understanding jack shit. That the only reason this crossover exists. If the concept was handled intelligently from day one, no-one would ever have this debate 'cause the false impression that Aliens will sit around and allow their asses to be kicked would never have taken root.
