There is a reason that you cannot. In Dom1 supercombatants were overpowering and had very few counters. So to compensate for that, they have made them more mortal to allow for variety in play and the game.

If you'd like to see how they used to be played, you can try playing Dom1.

I prefer having to work to keep my commanders/combatants alive by using a variety of tactics and spells rather than just making a plow to run everything over.