Machinist is arguably the biggest let down of a class/job ever to me

[Elnidfse]

Only if you do it by accident at the wrong time. It's a DPS gain if intentionally overheated during Wildfires 3-5-7-9+ or it's excellent to naturally overheat while AOEing trash packs and then using flamethrower to snapshot the bonus damage on the last second of Overheat which will then carry you all the way past the 10 second removal of GB.

And then there's obviously intentionally overheating before boss invulnerability or phase changes.

With the two bosses we have right now. That's not a good idea or possible. Goin hail mary on an overheat to squeeze out a tiny bit more damage before kill is a better idea, but you'd have to unsync your FT for that and/or setup a lineup that will allow you to deal damage at the end of your overheat before the boss dies or suffer a DPS loss.