- Units in Heroes 3

1. What damage value of the units was used for the calculation? For example, the Royal Griffin has 3-6 damage. What do we use - 4.5?

Yes. We use the average damage.

2. Cyclops King 2.664473684
Manticore 2.662907268
Practically identical characteristics with different attack, defense, and damage values. Coincidence?

No, it's not a coincidence:
-------------------damage---attack--defense--hp
Cyclops King--18.00--17--13--70
Manticore--------17.00--15--13--80
as you can see, 5.8% more damage, 13.3% more attack, but 12.6% fewer hit points
And if we put them in a sparring match, we get:
Manticore deals 18.7 damage to the Cyclops King and "kills" him in 3.743315508
hits, while
Cyclops King deals 21.6 damage and "kills" him in 3.703703704 hits
i.e., Cyclops King is "stronger" than the Manticore (considering only the main parameters).
So, we consider the result acceptable.

3. If we compare these two units using the specified calculation formula, will the result be close to one?

"-Hello, is this the residence of the Stupid family?"
"-Eee, aaa, I didn't understand the question?"
That's how I feel.
I didn't quite understand the question. :)

P.S. I think a table would be much clearer if we rounded the numbers to integers. Let's take the Peasant as 1. The Archer would then have a score of 92166 (according to the rounding rules).
Cyclops King - 3466
Manticore - 3463

Yes, yes, that would definitely be better. But! Our benchmark is not the Peasant, so HE (the benchmark unit) should be 1 for now. And after the final result, we can transfer it to the """System S""" :)

P.S.
I wanted to attach a file, but I can't figure out how to do it yet. I'll try to figure it out...