I'm pretty sure the survival levels are hardcore because of the fence. The levels could be exactly the same, no changes at all, but they would be easy if it weren't for the HARDCORE fence. It's all in the fence guys!
It's very annoying how so many people complain about the little details that make this game "unplayable". This game is way better than the comments make it look.
I'm gonna transmit your question to them and see what they have to say.