Mordheim, but honestly any tabletop game, should really be played as a narrative instead of a tournament.
So, if a warband becomes overpowered, throw something their way to level the playing field. Make an unlikely alliance with another warband and go 2 versus 1. Write a special scenario where the stronger warband is caught into something such as a zombie infestation, or worse, where you play the "NPC" gang.
Most fun I had with Mordheim was when we did narrative games. And if there are people that don't like that, they really should be playing something else, like Shadespire.