Dismantle was among the best mitigation, if not the best.

60s second CD, 5s debuff and 10% reduced damage. You can argue that Tactician is better because you don't need a target and Dismantle applies to a single target.
But there is much more content where Addle (90s CD) is more powerful than Tactician. Still, Tactician/Samba/Troubadour should have been 60s.

Flamethrower, interaction with Bio-Blaster wouldn't fix how boring the skill is. It would be a simple damage buff but Flamethrower would remain a meme action that requires to not move. Either the combo is too weak for single target, either it's good enough and the rotation would be that 1 Drill out of 3 has to be replaced with Bio-Blaster + Flamethrower instead. It would be boring and wouldn't fix FT even if it adds 2 buttons on ST rotation.

Gauges, a massive problem with both gauge is that there is only one button that use those gauges. Queen for battery, Hypercharge mode for Heat. Due to how the Queen works you would need more battery generation and a really strong action that consume battery, or a 3rd resource that is filled based on the battery spent for the Queen. We generate too much heat, so yes that's the best gauge for a new action consuming a gauge. But the more heat we spent, the more boring 1 2 3 we'll get. IMO, wildfire is a good candidate for a heat spender. Spend heat and slap a bomb that explodes on the target and (finally) deals AoE damage. Not like AoE damage on Wildfire was requested for a long time.

And yeah the 1 2 3 is extremely boring and they definitely need to fix that.
Overall the MCH has very good new ideas that doesn't works well with previous MCH. I don't know if they lacked time or didn't wanted to rework the MCH further but we can clearly feel that the new rotation conflicts with previous abilities, Wildfire and Flamethrower being the one that stand out the most.