With regards to frontlines, speaking very generally here:
NIN is low risk, high reward
DRG is low risk, reasonable reward
MNK is high risk, high reward
SAM is low risk, low reward
When you play melee in FL, you are basically always evaluating what you can get away. Like, OK getting this completely isolated player is simple enough, but can we pounce upon a healer or something that is just a little over-extended? For NIN and DRG it is very easy to get in, very easy to get out. Like with DRG we literally get to cancel Holmgang on a 30 sec CD. With MNK, we have a shorter gap-closer than DRG in exchange for being stickier in-combat, we have no exclusive escapes, and no ranged attack to build resources or stay safely engaged. When MNK carries a game, it is usually a very scrappy environment where melee is always on-top of the enemy and then MNK burst is out of control, making it the most inconsistent as far as scenario and battleground is concerned. SAM on the other hand, while of course all melee have decent blowup to varying degree, I find the way SAM taxes healers doesn't translate as well to FL. At the very least the movement action is more versatile and the defensive CD scales with pressure.
