hmm this is a cool solution to that actually. I kinda like it. Doubling troops health would make for interesting dynamics, like archers being weaker just because they can't kill as many and as easily (and we need that). Armor more effective... and yes, battles lasting longer. Can easily be a mod, but I think it would be worth a try that developers test this and maybe increase health of troops per total and see how that goes. Or give difficulty options more freedom of choice (like reduce damage 2x for friendly troops and enemies, instead of it being a one-sided thing. I get what you're saying, you don't want an easier game (you want it to remain fair) but also want battles to last longer. Personally I wouldn't want so little damage dealt to me that I turn into a hedgehog like in second image, but a little more tankiness to troops would maybe be good.
If attributes also gave health (endurance) then higher tiered troops could have more health. And it makes sense, since they exercise more, eat more (well, they should eat more than a peasant really, so maybe that needs to be a feature), and would make at least high tier troops more tanky in general. Archers would deal more damage etc, because Control and Vitality would give damage let's say