Okay, I agree with almost everything he said (for what he typed out) except the order of difficulty. The difficulty in any job is somewhat false it's usually people think of their initial learning curve/experience as the indicator that this job is hard, but I will say I've never had issues playing monk or any other dps outside learning the initial rotation. Anyone who says MNK is hard due to positional is making a mountain out of a mole hill.
The harder class to play is ninja because regardless of positional requirements you need to be aware of your dot cycle, other people's TP, your TP, huton recast timer, back positional for trick attack, kassatsu timer, suiton/ta timer, and MUDRA LAG. Also if you cannot get in around 12-13 mudra casts in a housing area before auto-bunny then your connection is having issues and your input lag will lower your DPS and cause other potential issues like accidental bunnies. Playing Ninja at the peak performance almost feels like it requires WTFAST or other pingzapping programs that help you avoid bad routing. So mudra lag coupled with the other things you must be aware of, while playing ninja, makes the job the hardest.
What you should play as a melee: MNK
What you should play as a caster: BLM