Do you prefer armor or attack?

For example, we have Shakti with a powerful stack of Trolls. For her, attack is much more important than defense because it’s very important to eliminate the enemy stack in one hit and not take any damage in return!

This is debatable. I am generally willing to agree for battles in Metro and against Blessing. If that's not the case, then with such a focus on attack, you will either fight weak neutrals or periodically receive retaliation. And 6 speed doesn't guarantee going first. IMO, Shakti's attack becomes unnecessary if, in maximum buildings (except for Merfolk, but there, precise calculations are possible), Trolls destroy stacks under Blessing. This happens around week 2, sometimes even week 1. Even I had a game where I got incredibly lucky and managed to sequentially defeat maxed-out Gnomes, Bank, and Fortress units in week 1.

If the stack is too focused on attack, they will target weaker units, leaving the main stack for last.

And when will this "last" happen in Fortress on grass? In the second round.

Units with retaliatory attacks would also benefit from this!

Really? Let's go through them: Harpies/Witches - they don't exist; they were already defeated in week 1, so it makes no difference; Nagas - given their speed, I personally prefer defense; Hydras - everything has already been said; Vampires - for those who huddle in a corner (their primary function), defense will be better; Cerberi - attack is better. That’s how things stand.

Oh yes, one more important point. If you have a Ballista, increasing attack significantly increases its effectiveness. For Gurisson, the Ballista generally tears apart everything!!!!!

Yes, attack is definitely more important for Gurisson, but he is just one hero, and not even the strongest. Even Barbarians still have Desa, Crag, Greckin, and Tiraksor. IMO, if you want to play as an artilleryman, play Heroes of Might and Magic V. It is possible there.