As Parnell, your best friend is Cabot; in lore, and game. When your aiming with your shotgun and rockets, move in close. Aim for the center mass, for 1.0 times damage. Avoid limbs, for they cause 0.5 times damage. While aiming at the body, always move in for headshots. Super Soldier, and Damage Amp; makes for some amazing open field damage.
Rockets are actually quite fast, but they aren’t always easy to land. Try to predict where the monster is moving, and shoot there. Takes some practice, and it’s still going to be hard; but you will get used to it.
I actually prefer Capacity on both assault. Parnell is amazing with more shotgun shells; at close range. More mortars on Torvald, make for some heavy long range damage. Only pop Super Soldier when you’re in close, and have decent aim. Especially when the monster is attacking team members, they will often be too distracted to avoid you.
Only use your shield, at around 15-40%, depending on how hard you’re being pressured. If you’re being targeted, and about to be hit by a rank 3 rock throw/warp blast; and your support can’t help, use it to avoid it.