It's not that simple. Let me give you an example of what balancing issues I've actually faced before.
We had several human factions, each one with a particular "speciality". One faction had air superiority, and in our story there was no high level technology, there was also no dwarfs (they just didnt exist in the story) so everything was powered by magic. So we had one human faction with these really strong anti ground airships and needed to balance this, to make it fair to all the other factions. Now let's make this simple, this is how tricky it is to balance things just between 2 teams. Since one side had strong air we gave the other side stronger anti-air units. The side with the heavy airpower had archers as anti air, while we gave a unit called spearmaster to the other that was slightly stronger in terms of both damage and hp. But this wasnt fully effective because if the airships were spammed it would leave the 2nd faction at a major disadvantage, plus the faction with the airships could pull certain harassment strategies that would be unfair. So to counter this we increased the food, gold and lumber cost of the airships, but that was not fully effective either. It took us a long time to figure out that in order to have a more or less stable balance between the 2 sides we had to give the side without the airships a flying anti air unit that could effectively counter any kind of airship attacks and to make this unit relatively ineffective against ground units so that side 1 still had air superiority.
So it's not as simple as just giving a unit an extra 100hp, it's more like you gotta balance one side against the other and do so in a way that still allows a side to keep its special units.