This is untrue, in fact by the time you're in full mythic you may well just be back to playing Arcane again.
It is not haste scaling that makes UM outpace Frost Bomb, it is Archimonde's trinket.
Archimonde's Trinket demands you cast a Frostbolt before every Ice Lance, greatly increasing UM's proc rate (as it greatly increases your number of Frostbolts).
What is the better lvl 100 talent for frost in hfc? If picking frost bomb or ice Nova.
You didn't give an answer about why UM was better, you said UM is never better until you reach Mythic. That's wrong.
UM becomes better than Frost Bomb for Frost with the correct trinkets and set bonuses, then stays that way. It doesn't require mythic gear.
I am the person who explained why UM will be better. You just said "it's not".
Would be great if those that have killed 12 or 13 hc bosses could give their advice on specs/talents for the 13 bosses, so lesser progressed players like myself can take advantage of that knowledge.
Far from a top mage, but through 13/13N and 11/13H here’s what I played. Frost on Assault, Council, Iskar, Tyrant, and Xhul’horac. Arcane on the rest.
During Mythic progression I’d imagine a couple of those Frosts will be Arcane instead. You aren’t going to compete on the meters on Assault unless you’re Fire, so probably just stick with Arcane for the better single-target burst on adds. Hopefully it won’t be too long before I just spend the fight running in circles spamming AE. God I dislike that fight already. Could go Arcane on Xhul’horac if the last phase is the hurdle, Arcane might be more useful on Iskar as well.
I'd imagine most mages will be Arcane/Frost during progression. Plus, I believe that Arcane gets the best boost from the legendary rings once we have them so that may seal it as the best spec on most fights. I could see Fire being played for padding on a few fights and trying to rank, but not that much more.
Fire's gotten really bad. Anyone still playing fire?
Actually, fire is pretty good now in decent gear and proper trinkets.
#1 on Archi M is fire mage for example.
Fire can also be top on a half of the HFC encounters:
https://www.warcraftlogs.com/rankings/8#class=Mage