I only had a couple of games and I'll take as true that Champions need tweaking but I must say that I do quite fine using normal troops to kill anything.
Bloodthirsty + Charge + Fast + Spear + Learther Armour set (to add some survival). Add the Sovereign and, if possible, a Champion (for special traits that benefit the army and because they can grow to be tanks/dps of legend... Verga was quite legendary mauling dragons in turn 1, inb4 nerf). Develop Groups whenever you have the chance (you want to level up Groups). With that setting, the unit can in most cases reach the enemy lines during the first turn and before the enemies can take their own turn.
My last game (Normal diff) most of the game only had my Sovereign and a Champion (that barely used) along 4 Groups of units like the one I said. The Groups gained so many levels (all level 15 by the end of the game) and were so effective in first turn assault (supported by some Leadership/Tactician), that I never missed the usual Champion Party Only. It's true that at end game they had lose some edge against stronger foes (basic spears, basic armour...) but were still quite good.
I'm quite sure that other type of units can do their role equally well if well leveled and properly supported by their Champion(s).
As for Champions...
Not having permadeath but some random penalties is quite nice to me. I have never suffered it yet but I have seen the enemy Champions broke their noses, lose ears, be amnesic... Quite cool. I'd say that losing a Champion and winning the battle should still have a chance of "penalty" (only lost one and still won so not sure how the system works there).
Some traits are must have (those +1/level) for obvious reasons. And you know what they say about content that is "Must have",