I've given up on the assassin and I think I'm about ready to give up on the Vulcan. I just can't seem to find a load out for either that I like. The Assassin gets taken out easily by the same light mechs it's suppose to be hunting!
Loving both Archers though.
I've only really had problems when outnumbered by heavier mechs.
The trick is to treat them more like light mechs than medium mechs. You always want to be moving at top speed from cover to cover to keep evasion as high as possible abusing your jump jets as needed or just sprinting if there's no good shots. Similarly, don't try to burn through a mech from the front, try and get behind them or at least to the side. That's less effective against light mechs, but also a bit less necessary.
As for loadouts: I have an assassin with 1ML, 1SL and 2 SRM-4s, one with 1 ML, 3 SLs and 1 SRM-6, a vulcan with 4ML and 2SL and another with a COIL-M and 4 SL
Just run fast, unload into the rear of whichever mech has presented it, and keep running. No focus fire, just taking opportunities. Again, though, when you're outnumbered evasion stripping starts to become hazardous for the vulcans at least, they can't build up as much evasion and don't have room for a gyro.
Again, though, haven't had trouble with lights really.