Because it is not balanced.
Video proof, yes?
[u]Why was blink strike's range (and perks) nerfed but this was left untouched?[/u]
[u]Why was Scorch Melee nerfed to shit but this was left untouched[/u]
[u]Why was Harambe murdered in cold blood when all he was doing was holding down the city?[/u]
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Stormcallers have no neutral evasive maneuvers, no unique defensive/healing abilities, mediocre grenades, and an awkward jump. Their melee and super are all they have going for them. If you're going to nerf their melee, then they're going to need a buff somewhere else to make up for it.