The challenges in 40k as far as I have seen is often used to merely prevent an enemy character from attacking your unit. If Mephiston for example charges a unit of kabbalites, then you just have a Sybarite challenge him so that he stays stuck in the combat. This is feeling similar to the wound allocation rules in 5th: not realistic and cheesy. Would a Guardsman sergeant for example challenge Abaddon for example when they met on the battlefield? Maybe an extremely couragous one would, but otherwise no...
In order to fix this, my mates and I have thought of a house-rule that fixes this:
"After a challenger has been nominated, that challenger has to take a morale check. If it succeeds then a challengee may accept the challenge. If it fails then the challenger has not succeeded in issuing the challenge, and may not challenge issue another challenge for the rest of the turn. A character that has to issue and accept challenges automatically passes this test"
In this way characters with low leadership cannot always keep powerful characters locked in combat, and makes the Champion of Chaos less painful for Chaos players.