A level 5 shouldn't be playing Iron Banner then, just as if you were level 5 you are excluded from level 20 strikes, or from going to Mars. Or a more sensible solution is as you said, tier off the levels. If a level 5 can defeat a level 30 with relative ease, how is this different to regular crucible and what of the people who put time into gearing up in anticipation for this event. Honestly, Iron Banner was the only reason I bothered getting to level 29.