I have done every fight on HC as arcane and there's not a single issue with it.
Klaxxi doesn't really involve that much movement, especially if you get lucky.
Siegecrafter is completely fine, you can invis the sawblade and you're not gonna be hittng the boss as fire either (not to mention your bomb does double dmg as arcane so that'll do more while you're running around). And you can stay within the same rune during magnetic phase easily. The fight is extremely doable as arcane.
With frost armour Thok isn't an issue.
Garrosh is really not problematic since the tactic now is to stack constantly, and a rune of power covers the Malice crap.