Current flamethrower deals 80 potency every second, for a total of 11 ticks with 880 potency over 10s. Scattergun alone deals 750 potency over 10s for 5 GCDs, then you can add the value in heat gauge (50 gauge so a full ACB hypercharge ready to use, and ACB alone blows FT out of the water in damage output).

ShB FT was very, very barely above the standard AoE rotation, and had niche uses in dual targets where it had the edge (barely). With the introduction of scattergun, the general AoE rotation gained weight while FT stayed the same. I really do hope they did something to FT for Dawntrail because opening the job trailer once more with FT without changing anything would be a joke of very poor taste after so many expansions.

FT used to be incredibly powerful in AoE for the expansion it got introduced in, when used in combination with overheat (+20% damage snapshot covering the whole 10s debuff of heat gauge lockout).