I don't get it that no one buys an archon. I just did in a ladder game. Maybe I am a bad player, but the enemy approached with an unstoppable paladin/dreadknight combo, and there was no money nor time build a grand archon, so the blue archon seemed like a good idea at the time. Of course, it did not work out, since just cancelling 6 points of each here was not enough. That is why I suggested 8.
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?