To summarise my question in one sentence: how do you kill people in lockdown when you are a gunner and DO NOT use pulsars or supernovas (both of whom are better at killing people than most swords)?
Lockdown and guns
mind, you, I'm a rather fast switcher, but more important than that is your choice of gun and class:
Use a cryotech (freeze) if you don't have teammates around or use charges often. Teammates break the freeze status, but it can be your savior when you're outnumbered. You do NOT need to (and maybe even want to avoid) do quick-shot techniques with cryo because a freeze can mean a free charge / kill.
Use voltech (shock) if you have teammates around or are a quick attacker. When people are shocked, they are vulnerable to multi-hit attacks, whether it be from your teammates or from quick shots.
Use firotech (fire) if you're going to die.
Nova Driver should be used if you don't have a status alchemer and are fighting non-elemental defense.
Umbra Driver should be used if you are fighting elemental defense.
Recon lets you sneak a first hit (and lets you gamble on casting status on first hit) if you shoot outside its warning range, and if you can warn-peek-deathmark, you remove their defense, making guns like the blaster line extremely dangerous (blasters are normally gimped because most armors have normal defense, but when you remove that, they HURT.)
use alchemers. Try to master weapon switching so you can shoot faster (see some tips here)