MMH5.5 - Heroes of Might and Magic 5.5

Gives +1/1 and also at level 20, +2 to defense if defense is present, and +2 to attack if attack is present.

In this form, the ability becomes much more interesting.

And is it possible to further enhance the counterattack?

Yes, but the mod authors stopped at these numbers (although I also pointed out that the bonus is very small).

And can the hero's attacks be enhanced with this ability?

Technically, yes, by temporarily increasing the hero's level number before the battle. But this will also affect specializations and some spells that depend on the level.