Well first you need to up the potency because it's weaker than Shattershot in it's current state.

But a true fix would make Flamethrower your Heat Gauge and make Auto Crossbow into an AoE Turret for Energy gauge.

As far as channeled casting, it's fine if you make it risk worth reward. Take DNC's Improv for example. Is it really worth eating an AoE for a Max Barrier and Regen buff? Same with Flamethrower. I would be nice if FT applied some kind of stacking Defense Debuff to the targets where is a stack would be a 2.5% with a max of 4 stacks.

But this is SE and everything is fine so back to wishful thinking.