Second stage of the battle. We inflicted maximum damage, killed about 50% of the neutral troops, and suffered almost no losses (single units). Finally, the remaining enemies get a chance to attack us.

I'm not a "pro," but that's not how it works.
First of all, you know that the AI has its own behavior patterns, right?
For example, a "Cerberus" will run to the maximum range to inflict damage, but it "fears archers." Its target priority is archers. So, if you place archers in the corner on the "first line" of your formation and place "single units" in the second row, not completely shielding the archers (there's access to them from the side), the Cerberus unit, located diagonally from the archers, will try to bypass the row of "single units" in hopes of reaching the archers on the second turn, not considering that they might be protected. Plus, you can sacrifice one "single unit" on the first turn to distract the Cerberus, which will give the archers a full-power shot. Plus, the terrain. Plus, plus... there are various action options during the battle.
If the enemy's speed is 4-5, the "single units" don't just go to die; they maneuver. They find a place to hide and then run behind the enemy, causing him to move back, meaning he loses two turns... Sometimes, retreating one square is enough, and the opponent also loses more than one turn (again, the AI considers the threat of a direct attack, and there are situations where it moves one step, losing the opportunity to inflict damage).

It doesn't happen that melee units of levels 1-6 can defeat more than 4 of your level 1 units (except for units with area-of-effect attacks). Mages and druids, yes, that's a problem. But defense against them won't save you; tactics might.

The "attack" bonuses do not apply to archers.

As long as there are perks for "attack," they exist. When/if they are reworked, it will be a completely different conversation.
Giving 30% to "attack" without changing the perks is not my idea. But I'm not the mod author