I don’t play frost on this toon but I can easily get into pugging 15s as arcane for weekly vault. If you are wondering about fire, I switched from arcane to fire for raid. When I tried fire a couple times in m+ this tier, I was reminded why I didn’t like playing it with pugs in 9.0 because most pugs pull conservatively and you’ll only have combustion up every other pull. Same deal with arcane but at least you will have RoP, RS, and TotM every pull when AP isn’t up.
Side note, I just saw the 9.2 ptr sims with double leggo. Kyrian arcane looking like the most versatile for single and multi target. The only drawback it seems is bombardment being way better than harmony at 5T. Frost is like a pick your poison type of deal with the different covenant and leggo combinations depending on how many targets. What is also concerning is fire and SKB simming higher multi target when in practice you will lose the stacks traveling from pack to pack in m+.