MCH are great due to their
insane burst damage.
In PVE they are #1 on the DPS rankings for the first 20seconds due to how intense their opener is.
MCH Opener Video:
Good luck keeping up with that's happening!
They can force
TEN ATTACKS in a row, all off global cooldown in less than 10 seconds.
As for their mobility, it works similarly to WM, except that their 1-2-3 combo has a 50% chance to proc on the first shot making the next attack instant cast.
This means 50% of the time using only their standard attack can they move around for 3 seconds.
Bards don't get that.
Machinists who plonk their turret on the node are sacrificing so much damage to be a nuisance and that certainly isn't their reason for being in FL.