GB should always be on for trash pulls as it seriously buffs our AoE damage. You should also be spamming Spread Shot whenever there are three or more targets on the field, no exceptions. Even if you run out of TP you'll still have put out more damage than you would spamming our 50% combo, and you can always wait for TP to regen between pulls.

Don't be fooled by the big numbers. Certainly, they look nice, but they mean nothing if they don't add up to an overall larger number than a bunch of small numbers.

Also, my auto attacks average 400 damage, so yeah, not sure what you're looking at. Maybe you're getting confused by turret ticks or something.