The only thing I've had problems with Gunnery Commando is if I can't get my stuff to crit. But if I get a crit rotation on someone, whoever I just hit is 100% dead in 4-6 seconds.
2-4K Grav Round x 2, 4-5K Sticky Grenade, 8-10K Demo Round, 4-6K High Impact Bolt = Dead. It's super rare for that to happen due to only have 25% crit chance but it's still highly effective if it doesn't crit. I absolutely love playing Commando now. I hadn't touched him in a year.