Flamethrower deals 80 potency per second. If you triple it, that would be 240 pps.
1-2-3 combo deals respectively 80pps, 112pps and 144pps. Heatblast deals 120pps.

If you triple Flamethrower damage to ennemy affected by Bio Blaster, the single target rotation would include a "Stand still for 10 seconds every 60 seconds" which isn't acceptable.
Flamethrower is barely worth anything, sure, but it had more problem mechanically than damage wise.

The Automaton Queen has even more problem. To put it simply, they can't do anything with it as adding a 3rd finisher would be even more troublesome.
AQ "finish" phase would be longer, AQ has already trouble targeting the correct target, AQ AI isn't able to seek another target for its finisher and will shutdown before pile bunker/crown collider if the target is dead.

As for its AoEs, who care about the number of buttons?
If Air Anchor had Fall-off, Wildfire had fall off and Chain saw reduced fall off, that would be enough. Don't had buttons that will be only pressed in 1 kind of content.

MCH clearly needs some work, Flamethrower, Automaton Queen, charges on HC/Wildfire, buff it AoE damage and the lack of utility.