In Heroes IV the damage formula was changed compared to Heroes III. It is now directly proportional to attacker’s Attack value, and inversely proportional to target’s Defence. There is certainly a big difference between having twice more HP and having twice more Defence: more Defence is better against ordinary attacks, as wounds will be twice easier to heal using spells, while twice more HP is twice better against magic, as magic is not resisted by Defence at all. It matters even for Frenzied Gnashers/Black Dragons, because if they had lower defence for higher HP, when fighting a hero with Grandmaster Melee they would get less damage due to GM Melee being able to reduce enemy Defence, but to no lower than 10.
With damage and Attack it seems to be a bit harder to judge. Well, heroes can get numerical, non-percentage based increases to Attack value, and their damage grows with level (if I am not mistaken), so it does matter for heroes — for example, +5 to Attack would produce a vastly different relative damage increase for a hero with base Attack of 10, 20 or 40.
However, I don’t remember anything that gives plain numerical bonuses to creatures’ base damage and/or Attack. Everything that I remember — spells, artifacts — increases their stats based on percentages, such as +25% to Attack. What if, for the purposes of clarity, their damage would be changed to include their Attack bonus, and their Attack would be set to some fixed value for all of them, or at least for all creatures of the same level? For example, if a creature used to deal 20-30 damage with Attack of 15, and another creature used to deal 10-30 damage with Attack of 20, the first could be changed to deal 30-45 damage with Attack of 10, and the other one — 40-60 damage with Attack of 10.
Would anything practically change except probably some rounding?