Really... Let's see how many removal spells they have
Cone of Cold
Mirror Entity (Counted because at the very minimum, this spell can counteract whatever your opponent summons)
and then finally, Vaporize.
4 of those spells deal area of effect damage. Then you have Frost Nova which pushes that number up to 5.
This would be fine, but there isn't a single one of these spells which come with any kind of penalty at all. In order for a Shaman or a Warlock to use this kind of board clear, they either need to damage themselves, their own minions, get overload or destroy cards in their hand.
Then for a paladin, druid or warrior to use this level of board clear, they mostly need to attack the enemy minion head on, resulting in the hero taking damage.
Let's also note that Fireblast, Fireball and Pyroblast all do exactly the same thing at varying degrees of damage. Same with Arcane Explosion, Blizzard and Flamestrike.
There needs to be some kind of penalty for Mages using all of these spells. I can think up about 5-6 ideas from the top of my head. Why can't you?