I do not know why people say that Josh Dallas is a bad actor. He can not be better than Ginny, Lana, Colin, Bobby and JMO. But he has given sufficient evidence that he is a good actor playing James, the fear of Charming, Evil Charming and we can see the differences between Charming and David Nolan. Just because he plays the good guy does not mean he is bad actor.
Personally, I think he is one of the best actors on the show and holds own easily with Ginny or Lana or the others, but that is just me.
I think he has gotten pretty popular in the show–if there are people that are saying he is not a good actor that is, in the end, their opinion.