Playing a Gunnery spec Mando in PvP just for the full WH set, i agree the interrupts are painful, if we dont get at least 2 grav rounds off our ramp up damage is more painful for us than who were aiming at.
Stuns and stun breaks are another problem, its irritating to be taken apart by an operative because he can stun more than you can break and break more than you can stun.
Squishyness, any good player can drop a Mando in short order, its like a lightsaber through melted butter in some instances, especially if you get dual smash'd or chain stunned.
However.
If i do not get primaried by everything red at once, i can put out very nice dps for what i get laughed at a lot for, running a gunnery spec Mando in pvp, grav round hovers around 2k non-crit and between 2.7 and 3k crit, FA has popped upto 4.5k in crit and between 2 and 3k non crits (with CoF,) Hib rarely hits below 3.5k with 5x grav stack and around 2k non grav stack and finally, Demo round, this baby goes for anything between 3k and 5.6k, 5.6 being my highest crit so far and i havent even started min/maxing or augmenting. many games i have even broken 300k damage.
The potential is there, the DPS is there, skillfully you can make a Gunnery spec Mando viable in PvP just frowned upon and AT BEST, fire support, helping your team carve up the enemy with grav surges has meant that by being rooted i was the line in the sand, doesnt work always and i do get rofl stomped occasionally, but if played right in support roll and not Schwarzenegger with a minigun ala Terminator 2, you can win matches. Especially if they ignore as they are too busy with your own melee kiters who take their attention away from range