BallLM. A mod that changes and improves the original game balance.

If the lethal blade is added to all units from tier 1 to 4, it's enough to gather an army of shooters, split them into ones, and simply take out the enemy with those ones. Similarly with melee squads: get 7 Furies, split them, and beat the enemy.

Your mod kills the game, because the individuality of creatures is lost, the significance of luck and morale vanishes, and the importance of initiative is reduced.

But the point is to improve the game mechanics themselves, right?

Focusing tactics and "ones" tactics are truly a cancer on the game.
Ideally, this problem could be solved by dividing into two classes based on defense — normal and protected; the first gives no retaliation at all, the second retaliates to all attacks.
Alas, technically only the latter is implementable.

The unpunished slaughter of everything and everyone by shooters is another problem with the game. Only casters are worse, who do the same but are even more powerful with small armies, and encourage the tactic of "marching with an army consisting of a bunch of druid squads" due to the idiotic damage calculation formula. Oh, and they ignore defense, for good measure.
In short, yes, it might help solve the problem. But, in my opinion, not really. Ideally, the range of combat spells and shots should be limited; then, to perform attacks, one would have to expose themselves at least a little to the possibility of a counterattack... But alas, that cannot be done. So you do what you can.

This is what I didn't understand... Can you explain the use case in more detail?

Same thing. And wouldn't the lethal strike contribute to dragging out the game by players using defensive races? Say, I'm playing as dwarves... Would I like it if both of my super-expensive and thick magma dragons were killed on the very first turn by lethal strikes? I'd want to drag the finale even longer and accumulate more of them until the time when lethal strikes no longer matter...

Isn't this a too defensive change? And in general, it looks a bit boring after the previous one.

These kinds of things cause slight bewilderment. Do you realize that after the previous changes, you literally need to re-balance the entire game from scratch? One point of initiative for nomadic centaurs is a drop in the ocean here; we need to see what actually happened and whether orcs suddenly became twice as strong (or weaker) than all other races.

All units that originally possess infinite retaliation lose their trait
possible solution: give them the combat griffins' battle frenzy ability, and add retribution to the griffins themselves.

All units with double strike (and its variations: cleaver and assault) have decreased in value, since they receive retaliation twice, with no compensation
I just can't think of WHAT could fix this... maybe give them a swift attack or simply bump up their stats...

Succubi lost their individuality and got nothing in return.
Give them retribution?
Wizards of some factions are still able to hit enemy shooters through shots at other units (though this could be considered a feature)
The ballista falls apart when trying to shoot an enemy shooter.

An absolutely unnecessary change! Not only do the "ones" return (now, however, with an emphasis on area attack), but also, for example, the demonesses' chain shot disables this ability. And the cave alt loses its uniqueness...

I just didn't catch the idea behind the change here

The cavalry charge of horses not under Axel loses its meaning — damage reduction above the charge
increase from 5% to, say, 25%

Too radical, it seems to me — morale has almost stopped playing any role. At least returning negative morale would be a good thing...

The poor thing already gets retaliation for every shot, while it can't do the same itself, and now its hp are being cut :D