Why are some alolan pokemon so bad compared to others?

I'm not even talking in competitive, just made it to the battle tree and got my ass kicked by Blue, only had a turtonator, decidueye, and A-Muk with a bunch of other weak shit I was training at the time.

They could barely fend off anything. Decidueye can't take a hit or do damage, Turtonator can't do any real damage and A-Muk is slow as fuck. They all have decent natures and had at least 3 levels on blues pokemon. I love them but damn.

also general question thread