You already said it but a lot of MCH are burning their "combo" and leaving other abilities out of their rotation leaving them with some meager damage. Since our combo is largely different from all the other jobs we can relax a little on it and still maintain DPS. Using any ability outside of your combo won't reset it. Instead, you get a 10 second buff so you can use time between combo pieces to refresh Hot or Lead, replace turret, etc. You can also "stack" Slug and Clean Shot. If you proc Clean you can do Split to load another Slug proc.

Also don't forget that many of your panic and CC abilities are off GCD.