As fire you only have to care about the big ones that force you to move far away or immunity phases, because otherwise you are extremely mobile during your cooldowns. Arcane sadly does not have that luxury, as even sidestepping costs you dps. In general I wish they would make PoM castable while casting other stuff, like fire blast, because by the time you need it it's already too late.
I'm currently trying to get into arcane again, after dropping it in favor of fire earlier this expansion. But it's hard. The mobility is just addicting. I considered going frost, but I loathe the boring thermal void spam builds. GS or go home - I also didn't want to start over as venthyr from 0. So far I like there being some actual structure in arcane harmony, spamming just 1 button wasn't particularily interesting, outside of farming trash in the open world. Edit: I also could never really capitalize on the strength of fire in m+, as my group of friends isn't doing big pulls to make fire actually worth it. I get more out of AB cleave as sad as that is ...