Holy Light Domain is by far the best utility/support skill a tank has access to these days.
Remember, not all groups run with a Warrior/Priest.
Well.. if one of the best supporter classes for rofl is overwriting the major support utility a tank class has, it's reasonable that ppl keep playing it, because in random runs you usually don't have access to a w/p, but it's not a good class in general. In our guild runs with an optimized raid setup, a K/M is just useless, as said. If the debuff is changed to overwrite W/P or even stack, sure, K/M would be very useful. But that's just one single class. Thinking about all the other knight combos, I stay at my statement.
Regarding K/M buff being overwritten, Lutine made a good proposal.
Knight/Rogue and Knight/Warrior both have increased light damage taken debuffs, which are very potent when paired with the right classes. Knight/Druid has a increased healing taken buff for the group. Knight/Priest has a battle rezz. You said yourself Knight/Champion has a pull/stun.
I don't see lack of utility.
Edit: Seems like Lutine was faster![]()