Heroes 5.5 WarGame Edition - Tactical Edition.

This is not a very common case of a Ranger with mini-artifacts.

In the original game, where players start with only one city, this might be the case.

Avenger 2 - increases the hero's direct attack (deadly shot)
Avenger 3 - the chance of dealing double damage to a sworn enemy increases by 10% (forest cunning)
Avenger 4 - all creatures of the forest alliance in the hero's army receive +1 to maximum damage

1) This is an existing perk.
2) This is an existing perk.
3) This is an existing perk.
So, you're suggesting "improving the racial bonus" by reducing the perks, but that won't work.

and if, at the same time, the number of skills within the "avenger" skill is reduced, then perhaps some underutilized skills can be used

Then it would be logical not to remove the perks, but to come up with other effects for the racial bonus. Attack is a basic element that is always relevant for elves, as all 3 classes suffer from low damage (10% chance for the attack parameter). And with investments in luck (+1/+2/+3 to attack) and the racial bonus (+0/+2/+4), the elf will be able to keep the attack at a level of 40%.

In general, of the acceptable solutions, I prefer the simplest ones. Once they are implemented, then we can think about improving them by replacing them with more exotic bonuses, having a live comparison of the effects. Undoubtedly, the most interesting solution, if possible, would be a flexible change of the racial bonus, or an elven ritual that allows you to spend 25% of your turn to change sworn enemies. To do this, it will be necessary to somehow remove the guild from the city and simulate the hero touching it, and upon exit, return the hero to the old place on the map.