Damage troops are better for even battles. But say you have a massive battle, say 100 squads vs 95. Even a small difference like that would be huge with a damage build. You can try it out in a simulator to test it out.
This build has 1 damage unit per squad:
Here is the same build, but 100 vs 95:
The tiny difference of squads in that battle causes a damage build to lose by almost just as much it wins by in an even battle. And the difference only gets bigger the further you go. That's what you were missing.