They don't scale up to the hardest enemies.
Yet again the confusion between player sucking and units/classes/games sucking.
Melee General with the right infrastructure can mow anything down with them. Multiplication > addition.
Please tell me what multiplier you are using to deal good damage when your unit has a 1d6 attack and the enemy has 7 DR.
It doesn't work. Level 10 melee general with 4 halls of strategy, a military academy and an arsenal and smithy boosting them. And Mariliths only have 5 DR, other enemies in that battle go up to 7. I'm not actually sure how the math works out, since there should be a 1 in 6 chance of them dealing 1 damage. My guess is that the Marilith actually has 5 damage reduction x 297 attacks = 1,485 DR applied to the whole attack, or something silly like that. You can see how the conscripts' 143 damage is never going to get through that DR. Yes this math is completely broken (not only shouldn't DR add up like that to the whole attack, it's being applied AFTER the to-hit calculation rapes your damage output), but that's how it appears to work.
Meanwhile Hellknights do this:
And can easily win the battle solo as long as you have some mana to keep healing them. Which is pretty cheap and efficient, even for mage generals its often cheaper on mana to just keep healing hellknights rather than directly kill with magic.