Heroes 5.5 WarGame Edition - Tactical Edition.

As far as I remember, a solution was proposed to "dissolve" the amulet when upgrading the Special Ability. That is, the amulet disappears, but the bonus remains. The Special Ability was specifically designed in WOGE to require a level 4 racial unit and an amulet, because that makes sense. Otherwise, a +1 skill level wouldn't be considered a great artifact for its price, and the situation with 4 perks on 3 slots is perceived as a bug. In addition, with this approach, the Special Ability is not tied to any other rigid upgrade or a high level of 20+, it can be combined with any upgrade (the requirements are only for the artifact and 3 racial perks).

Added 42 minutes ago

In general, I have an idea to make the classic racial skills not the main ones, but secondary. The main skills will depend on the class (warrior or mage). For example, for the Union:
Combat class - Ranger. Main skill - some kind of "combat training" that enhances the hero's combat parameters. And as a bonus, something for movement (Rangers are still scouts and wanderers).
Magic class - Druid. Main skill - something like "Knowledge of Nature." Summons magical creatures to the army. Fairies, nymphs, satyrs, unicorns, pegasi, and other similar creatures. Of course, in order to summon high-tier units, the hero must be well-developed.
The class-racial skill, Avenger, would then be secondary.
But, since one skill is already in use, 6 base skills will be too few...

The remaining 5 base skills are not a problem at all; they are usually enough. The problem is that I don't see any benefit to such a change, other than simply creating an additional class distinction. I perceive this as multiplying entities unnecessarily. It would be different if it had some fundamental strategic interest. For example, the very presence of classes allows you to play the same race in different styles, through different skill profiles and stat distribution. In TE, transmutation and mentoring are used for the same purposes. If that wasn't enough, then we could think about new, additional tools.

By the way, I also don't really like the idea of Debuffs as separate skills. I think about how they can be implemented as perks within one skill.
For example, such a perk as "Strength against Magic" is implemented by a skill. Level 1 - basic effect of the perk. Then you can increase the HP of units by 5/10%. And the perks in it - Debuffs. With effect adjustment.

I don't like it either. But such a solution is close to simply cutting off the debuff skills, because only 8-9 skills remain instead of 12 for the Orc. It is better to make the debuff skills useful by adding combat effects to them, so that the other races would envy the Orcs, and not vice versa.

The first 2 tiers immediately by default also greatly help in the initial rush.

Not the first 2 tiers, but any 2 tiers, depending on the specific hero. In general, the situation is complex. From the point of view of the "Cursed" skill, 2 looks good, but from the point of view of the perks of the "Cursed" skill - 3. The rush itself is not a serious argument, because it should take a back seat as the most routine and least interesting element of the strategy. Therefore, it is important to ensure that the perks have a worthy application in key moments - battles against another player.