Late-game Town Enhancement.

With an attack speed of 8, there is only 1 cell available to attack the second row of the enemy. If only 1 unit stack is within range, then the "dance" tactic is not justified. With this tactic, there are 5 cells and one cell from which you can reach the first row.

To understand how important the extra cell is, we need to consider just two questions:
1. What is the probability of hitting only 1 unit stack with the "dancers" without using the tactic?
The answer to this was given earlier. If you don't mess up the positioning of the "dancers," take into account the ranged units, and the typical enemy formations, then this probability is 0.2-0.3. If this is not immediately clear, you can take a piece of paper and arrange 3 large and 4 small stacks of each faction.
2. What is the proportion of damage dealt by the "dancers" (let's assume they hit only one stack each) compared to the total damage of the entire elf army?
Everyone either reaches or shoots; the stack itself is not the strongest. For damage, it accounts for about 10%. This means that by using the tactic and guaranteeing damage to another stack, the total damage increases by 2-3%. Even if it increases by 5%, the choice for the Elves is simple: accept one-time damage that is 2/3/5% higher or always deal 10% more damage. The choice is obvious; arguing with mathematics is pointless. An attentive reader might object: what if the damage of the Elves is 2-3 times greater (due to initiative, Wing, attacks on multiple units at once by the Elves, and problems with random elemental effects for the Elves), then maybe the tactic is more beneficial? It might be, but there is no point in discussing this scenario because the Elves will not become more resilient, which means it is a 100% loss for the Elves, whether with the tactic or without it.

Ents also want to move far.

Ents can reach their targets even without the tactic. Two flying units allow the Elves to easily find suitable terrain for the Ents, and their large size always provides options for choosing targets.

The "Infantry" tactic can also be used to counter the "League" tactic; no one forces you to place units in the third row.

You once said that the Elves need the tactic to block the Demon's "Tactic." I showed that this is not necessary; let the Demon be placed in the third cell. You say that the Demon will counter the Elves' tactic with its own. What is the logic? If the Elves' tactic will not work anyway, and the Demon is not planning to use it, then why should the Elves take it? There is another harsh fact: the Demon can do whatever it wants with the tactic, simply by taking Nibros, if necessary. This makes the "Tactic" even less useful for the Elves against the Demon.

If there are many artifacts for initiative on a high-initiative race (not against Wing or Mage), then you can be very confident.

If it's not Elves or Mages, then who is this "high-initiative race" against the Elves? The next highest initiative is the Demons, and there was a specific example of this above. All the others are not much more initiative than the Elves.

Let's say they destroy one stack of Fury; then the Orc will come and destroy much more.

More, but how much more, specifically until the turn of the Lizards and Dragons. The question of WHO the Fury destroyed is very important. If, with the tactic on both sides, the Fury destroyed the leaders (or, even more optimistically, Cyclops with luck), then the Elves still have a chance. There is no one to counter the Cyclops; the most dangerous stack is the Warriors.

Laser Cyclops have an extra point of speed and will reach their target without problems (in the game, only Cyclops with clubs are used); they deal less damage, but their damage is enough against the cardboard "League." If the Fury one-shot one stack of Orcs, then the Warriors will be on the first Fury with +2 speed, and it is not certain that the "League" will be able to reduce their speed. Darkness can interfere, yes. It all depends on who outsmarts whom.

The "League" is indeed fragile, and the Orc is a very inconvenient opponent for them; there is no dispute. All the tricks with "SA" or "Darkness," relying on randomness, and other tricks are all aimed at achieving the previously mentioned probability of victory of at least 0.3.

In the late game, Chaos can be ignored. When playing for a "build-up," 5 "build-up" from the leaders and the Cyclops will quickly reach their target and deal damage, especially if they are well-morale-boosted. The Berserk shield and the skillful "Darkness" spell are essential. This strategy is overpowered and cannot be countered.

I hope you wrote this in relation to the Elves/Orcs matchup; then it will just be a slight exaggeration. The Elves will still have a chance. Against other races, the "build-up" tactic is a particularly perverse form of suicide.
But let's return to the Elves. Against the "build-up," the following are taken: "Outcast," "Tactic," "Defense," "Darkness," "Education" (by default in the late game), the Lion set, and the Necromancer's staff (can be +ring).
The Fury go first, and with their boots, they destroy one stack of leaders.
Then, as a rule, the Elves' hero goes, and specifically in the following ways: morale on the Fury, good random on the hero, good random on the Stalkers + morale on the Stalkers. In total, a probability of at least 0.7 is achieved. Then, "Subjugation" is used on the Shamans, who will destroy another stack of leaders, and at least one will remain after them.
This means that the Orc has 4 "build-up" left (3 stacks of leaders + hero). The expected value of this scenario is already less than 2 hits from the Cyclops BEFORE the Elves' damage-dealing stacks start to move.
Moreover, there is a 25% chance that there will be only 1 hit. In this scenario, the Elves' losses with "Defense" will not be critical, which means that the desired 30% probability of victory is not so far away.
With 2 hits, everything will depend on the "Luck" and "Stun" skills. The outcome is probably in favor of the Orc, but there are options.
With 3 hits, the Orc wins for sure, but the probability of this scenario is 1 in 8.
As a result, the Elves again have about 30% chance of winning if they guess the right upgrades.
There is no particular advantage of the "build-up" tactic compared to simply placing the entire army in a standard formation.

However, it should be noted that all the current and previous arguments are valid in scenarios where the Orc starts on level 0 of Fury, i.e., 1 castle against 1 castle (without "SA" and the amulet + "Overload" combination). If there are 3 castles against 3 castles (2 castles against 2 castles with "Overload"), and the Orcs start on level 1 of Fury, then the Elves' chances will plummet.


Added 10 hours 27 minutes ago

You also need to have time to press "Readiness," and it only works for one counterattack.

I am aware of this sad fact.
But it gives the right to the first strike; with a good attack, this is generally pleasant; it interferes with the Cyclops.
However, "Readiness" is not taken only for this. Almost everyone takes it from "Sturdy Defense." And the larger the map, the further into the late game, the more powerful this skill becomes, which, of course, you need to have time to press. Therefore, "Readiness" and "Sturdy Defense" are by no means a panacea, but they can regularly help.