Frost in arena

I heard from multiple sources that Fdk is in 2s on a par with UH spec.
Frost is supposed to be better against warr/Hpala while UH is more effective against caster combs.
For some reason I never see Frost DKs on Warmanes ladder while back on AT they were quite common even in patch 3.3.5a (they were OP in 3.3.5b).
So I thought that UH dominates because of Smourne but even on Frostmourne nobody plays Frost even though Smourne is not accessible.
Why?

could be multiple reasons. switching specs. current available gear sets. tier bonuses. the list goes on.

also generally speaking in arenas rot pressure and mobility is always better than just dps. as a rogue main outside of dance your damage is mediocre, but because our mobility is always at 200% we make up for the lack of damage. as a frost dk you have howling for kiting, but it requires LOS. as a UH you have dots and pet dmg.