I will say about KFM that I have no goddamn clue what I'm supposed to be in a party. I've been told they can build either tank or DPS. They do have some threat-generation upgrades on their skill tree but I imagine it would be really hard because so much of KFM's defense is front-loaded onto their Counter ability. As far as DPS goes, I don't know how it compares to pure DPS classes like Destroyer or Force Master. At least with FM it's exactly what you expect it will be.

I've also read that KFM got hit hard with damage nerfs that drop it out of top-tier play, but being a new player I don't really have a baseline for that assertion.