Why is he so chubby. I dont think he is ready for top competition, but lets see.
Dude, the guy is a HW. You've been watching too many LHW or below fights. HW is for guys who are too lazy to cut weight (not really, but lol).
Look at guys like Fedor, he's ALWAYS had a bit of a belly, yet he's ALWAYS shown great cardio.
I think people have simply seen too many steroid pumped athlete/models and have forgotten that most of the guys who used to be the "real athletes" looked more like Cormier than Alistair Overeem.
Having a small amount of body fat actually assists in making muscle mass easier to maintain, as your body during training will have fat to burn rather than little fat and mostly muscle mass. Its also why you see most power lifters with a bit of fat simply because it actually helps more than it hurts.
While looking like a "Greek God" is certainly possible without PED's, the reality is that most guys these days who do (and are professional athletes), typically are using them to help maintain that look. I dont think guys are using PED's all the time, they simply use them between fights and cycle on and off throughout the "offseason"(whenever that may be for that athlete)
As for Cormier, yes, I think he's got a legitimate shot at being the next champ. Great wrestling, a great camp to improve the striking game, and clearly a level of honesty and intelligence that will make him recognize his own weaknesses and strengths and seek to improve himself.