Battle tactics against creatures on the map.

Tactic 1 is sufficient. Presumably, we eliminate the neutrals at 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 under Stone Skin and Regeneration (both effects last for 5 turns) runs forward and gathers all enemies around them, bravely enduring all their attacks. I think with 3 heroes, you can gather a couple of extra dozen guards?

Meanwhile, the crossbowmen slowly kill the neutrals under the effect of "Onslaught."

This is closer to my understanding... :) It's somewhat familiar from the Ghosts and Destroyers. Yes, specifically at level 5 (I choose the hero development "very fast"). And I know how to buy 3 heroes at the start. :)
Just one more question. I reviewed everything, but I couldn't find "Onslaught." What is "Onslaught," what kind of skill is it, or is it some kind of technique?

Added 17 minutes later
It turns out that Guards are born with high levels of Blood and Tears ;) I'm kidding. But their "Defender" ability is almost like "Sacrifice." And what about "Vigilance," is it like a second attack under Morale? Does it really work?