I find that after a certain scope of levelling which would then spawn large amount of enemies, the best option is usually using your 6 troops as meat shields and dispatching all enemies by yourself actually works best.
The thing is, archers don't seem to help because there are so many enemies continuously spawning in turn that after a while, eventually, a javelin or arrow just kills them anyway. Especially when your boys are trying to fire back or reload their weapon, they are just skewered in time. And if they are normal troops, not companions, they end up flat-out dead.
Therefore, I just bring my companions with high HPs and decent shield attributes, give them a strong board shield, and make them bait and soak up as much arrow/javelin fire as possible.
After you dispatch the first couple of enemy groups, make your companions hold position in a position very visible from the spawn points, and also with no spawn points at their rear angles. The newly spawned enemies usually take notice of your companions and just rain down volleys.
While your companions soak up those volleys, you take use of the terrain and snipe the enemies one by one, or close distance using trees/rocks as cover and take them out one by one. Since them bandit types usually suck individually, with a good shield taking on about 3 enemies at a time should pose no problem at all.