No one has debated whether it's currently too strong in AoE situations (except through whataboutisms reliant on dungeons always being dogwater), but simply whether any element of flavor of its healing-per-hit should remain. I have argued it should, since it's iconic to Warrior, but at diminished returns (directly, as per a modifier after the first enemy struck, or indirectly, as by healing for a % of damage dealt).
Scaling factors and tuning are not the same thing. Yes, Bloodwhetting is presently just slightly overtuned for all content and overperforms greatly in dungeons because its per-target scaling is so excessive, but those are separate issues. Were its initial tuning better, by nature of offering the smallest increase to max eHP of any of the on-demands, it would have room at least for some degree of unique perk or feature. It just can't be so ridiculously strong as to have a 500% bonus across an entire content type.
And yes, Holmgang shouldn't be any more than 2min shorter a CD than Hallowed, especially if Holmgang's core benefit across typical content that would benefit from an invuln of any sort is just the death prevention, not the healing spared.