Heroes 5.5 WarGame Edition - Tactical Edition.

The restriction that doesn't apply to neutrals – is it a technical issue? Or a balance issue?

It's a technical issue, but it's also interesting; the perk is still relevant for clearing maps (it has an alternative effect).

It's kind of weird. I mean, it's clear that units with a size of less than 20 won't accumulate using this scheme, but still... Especially combined with other, not the weakest, skills in leadership (attack is no longer needed for retribution, and defense is also moved to leadership). I don't know, it's crazy. You pump up troop recruitment, charisma, and defense, and you become invincible.

That's great. According to my calculations, the perk is balanced, considering the increased game pace (and the 2-3 times reduced troop sizes as a result). In reality, only 1-3 tier units will come from this perk, and since the player's army grows over time, previous increases become relatively cheaper compared to the current time. And if the player drags the game on for several months, then it's a different balance; let them take recruitment and not take chaos; it's impossible and unnecessary to balance everything for all timeframes. Can the perk be countered by entering the early or mid-game phase? Yes. So everything is fine.
In the original, the game lasts about 4 weeks (if you don't drag it out); here, it is planned to be 2-3. The base movement range is increased by 1.6 times, and experience gain will also be accelerated (approximately +1 level per day), and city thresholds are reduced by 1.5 times (from 3 to 2 levels). This significantly affects the balance of time and perks that are spread out over time.

Charisma, defense, empathy, retribution – all are very good perks, but the base of leadership itself is weak, and this is how it is balanced.

I would make troop recruitment either 10% per week.

I would throw such a perk in the trash. You'll get a couple of peasants 1-2 times per game, and that's it. The trick is that if perks are not desirable, then what's the point of them?

How do you manage to implement such things? I want to too...

By setting the properties of the enemy hero (initiative and speed penalties).

Added 4 minutes ago

Cool. It was already difficult for the Warlock to win in the late game with his focus on destruction, and now they've cut him by another 50%...

Don't rush; occultism (racial skill) has been strengthened to +1/2/3/4 to magic and knowledge, and also ignores 20/40/60/80% resistance (instead of 20/40/50/75%). In addition, the perks in chaos have been strengthened, but more on that later.
Also, the sorceress is now taken at level 2 luck, does not require a dark ritual (saving 2-4 levels), and grows immediately with +4 luck instead of +3 (because of the bonus from Energy of Luck).
In addition, the sorcery branch will also be strengthened (+1/2/3 to magic), but I haven't gotten around to writing it yet.
Finally, the base of luck (even though it has been reduced to +50%) is very strong: it gives an additional +1/2/3 to attack (in the original, it's +2/4/6), and a good bonus to combat.

I suggest that you don't compare it to the old skills yet, but only among themselves – those that have already been presented. Are there any unattractive skills or branches in them that are not interesting to upgrade?

There are already skills to protect against fire. For example, in the light branch. At the same time, other elements are somehow ignored.

This is the same skill from the light branch, only now it is much more useful and not so narrowly specialized.

Leadership skills are too overpowered, almost all of them.

That's how the perks should look. Compare it to any other skill. For example, attack (+10/20/30% instead of 5/10/15), battle frenzy (almost doubles the damage of low-level units), mass haste (initiative increases by more than 2 times, and it's area-of-effect).

Also, keep in mind that in WGE, stats play twice as much, since they are balanced in this way: attack and defense give a 10% bonus for each unit of difference, and magic is strengthened and depends more on magic and mana. So, the same +2 from the "Fireproof Armor" perk is a big bonus, like +4 in the original, plus the defense against fire itself.