With mixed breeds, it depends on the mix. You can't just say "Yes all mixed breeds are easy to train" or "no they're all thick" because it depends very much on the breeds in the dog's mix, the personality of the parents and the personality of the dog.
Some pedigree breeds can be more difficult - however again, this doesn't apply to every single dog. Someone might own one of the more 'difficult' breeds, but find they trained it extremely easily, or vice versa - they coulda bought an 'easy' breed to train and be having an absoloute nightmare with it!
I think it's just the luck of the draw really
