Are you making sure you're eating enough in order to grow muscles, also for definition the most important thing is a pretty low body fat percentage (not something insane like 5%, but probably ranging from 9% to 14% depending on genetics of course).
The most important part about getting ripped is indeed the nutrition, whether it be weight lifting or calisthenics, if you're eating junk food every day or something like that you won't really get the results. You must get in high quality protein, healthy carbs and fat.
Now, you shouldn't feel bad, genetics play a big part, Chris probably has a lot better genetics than most of us, but, if you see any results, and I mean ANY results, you should feel proud, I don't care if you gained 0.5 KG of muscle or 5 kilos of muscle, as long as there are results and you feel happier, healthier, and stronger than you were, you're on the good path.
The triceps plays a big role on the muscle up, do a lot of exercises that "isolate" the triceps like tiger bend push ups, tricep extensions, diamond push ups.
You also must progress to harder exercises, or as you said heavy exercises, or do more reps of that exercise, because your body kind of gets used to the exercise and your muscles become less and less affected (they still are affected but not as much), so to break your muscle tissues that they grow back stronger and bigger (here protein plays a big part, so they can grow), you must either do a heavier exercise (for example instead of pull ups, do explosive ones to get your chest over the bar), or do more reps (instead of 5 sets * 6 reps, do 5 sets * 7 reps, you get the idea).
That's all I can think of, I know this is long to read, but you'll get the muscle up, I bet it, keep going hard!