
How about this idea then:
Make all negate heroism work similar to warding. Instead of cancelling a fixed 6 points, make the archon cancel a percentage of leadership and chaos. Therefore it would affect HorseLords and Rangers more than it would affect Paladins and DreadKnights.
I am not sure what percentages to choose, but something along 50%-60% and 75%-80% for the currently priced archons might be an idea?