Several good points brought up in this thread.
First, no doubt the depth chart is being used to push Harper a little bit. No doubt he has some talent, but it could be that he needs to continue to mature. I think he'll be fine. Plus, even though he was here last year, once the season started he was likely a scout team guy, so while he was learning wide reciever skills, he wasn't learning our offense. It wasn't until the spring that he would've been full time in our system, but that's not any different than any transfer/red shirt. I have to think that starting out at QB at Oregon probably slowed him down a bit as well, but again, I think he'll be fine with time.
I've heard great things about Thompson, similar to Banks, but probably faster and a much more knowledgable about the system and what is expected of him. He has a chance to be an impact player.
As far as Smith being a return man ahead of Thompson, a lot of times it takes time for younger guys to get the return game figured out. I imagine before he's done here Thompson will be a very good return guy, but I think Smith will be too.