I don't see anything wrong with comparing units from different factions. After all, people discuss the strengths and weaknesses of various creatures. This is especially useful for beginners who think that the main strength of an army lies in high-level units, although discussions make it clear that the strength lies in the details, and it is sometimes better to sacrifice building Archangels in favor of training an additional hundred archers. And accordingly, for such an army, the "Bless" spell from the first level will be more useful than, say, "Meteor Shower." So, even by taking things out of context and making various assumptions/limitations, you can discover a side of a unit that you wouldn't notice in a normal game.
As an example, I'll share my own experience. I played a very interesting single-player map where an area rich in artifacts was guarded by a hero of maximum level with stats of 100/100/100/100 and an army of 999/999/999... black dragons, and he was called "The Law." It was assumed that it was impossible to defeat him and that you just needed to choose the right moment to avoid meeting him. A Necromancer with a couple of Vampires and a fight to the last turned out to be too much for such a monster. When raising the dead, the unit's hit points decrease to 1, and when a Vampire reaches this level, it becomes almost impossible to kill it. The dragon hits it with tremendous damage, but one Vampire still remains, counterattacks, and there are two of them again. And the Vampires attack the dragons in such a way that they both retaliate and burn each other through. The battle was epic and allowed me to see new aspects of the game mechanics in action, although in an online game with a live opponent, it is unlikely that you will achieve such an effect.