Tactic 1 is sufficient. Presumably, we eliminate the neutrals on level 5?

There is also a tactic against slow melee units with physical damage (who won't reach our crossbowmen in 2 turns) – a stack of guards with Stone Skin and Regeneration (both effects last for 5 turns) runs forward and gathers all the enemies around them, bravely enduring all their attacks. I think with 3 heroes, we can gather a couple of extra dozen guards?

Meanwhile, the crossbowmen slowly kill the neutrals under pressure.