Power Buildings

But there's a difference when, for example, you lose Berserkers or Birds.

The difference is very significant. Berserkers lose themselves on the battlefield (they're just crazy).

If you have to choose on the battlefield which unit to sacrifice, it won't be as painful to lose a unit with a higher growth rate.

Again, Birds have a growth rate of only 3 (or 5 with a menagerie and nobility). Berserkers have a growth rate of 19.

but in war, there are no battles without losses! ....

If there's a war, but there are no losses, then it's not a war.