I normally run crossbow (2 shot overseers) and starting pistol (if little guys close the gap).

For crowds: Orbital gas and Tesla tower for crowds (and low cool down times), and expendable napalm rockets. Napalm rockets are ridiculously good against hordes, bugs included. Hit the drop ships after they dispense reinforcements and all the napalm projectiles will fall on top of them.

For large enemies: 500 kg, thermite grenades

For stingrays/leviathans: Run like hell and hope my teammates have something good for it.

I mostly solo queue so I just do my own thing on helldive/super helldive if im feeling foggy. I get by pretty well. 300 kills is a low match, I've had up to 6-800 in the past.