Campaign is kicking our butt!

We just started playing about three months ago and I think we're about 4 missions into the standard box storyline. We're only using the characters that come in the box. We have a dedicated player that acts as full time Imperial (he also the owner of the game). He does most of the studying and instructed us how to initially play and how new cards work etc. Thing is the campaign just destroys us every single time. It's not even close. Just when we've cleared out some Imps he brings back three, adds an e-web, two elite probe droids and three Trandoshans. It just seems impossible and some of the gaming group are getting annoyed. Is this a problem for anyone else's groups?