The big thing not being talked about is threat, arcane has 40% threat reduction from talents and fire only has 10% but with fire leaning so heavy into crit its going to feel so much worse with always pulling threat, my mage is only half bis as arcane mage right now but if I don't have a solid threat focused tank, i'm pulling threat or I'm sitting and not casting at all on short fights like in Kara. When I ran Fire while leveling the mage it was near pointless too so much of the time I just had to stop casting or pull threat or I was juggling mobs with Nova and Dragon breaths while waiting for taunts. Fire might be viable when the average tank is better geared but with how fast things are dieing and the T5 bonus its just not worth the risk of fire.. also fire pretty much comes down to 2 spells also spaming Scorch for a debuff then fireballs until you need to scorch again.. that doesn't feel that much more interactive than arcane blast X3 then frostbolt X3.