Firstly, in reply to the idea that monks defense is bad because all they can wear is bracelets... well, thats why their defense is bad. If you equip any armor on them, they are crap... but with NO armor, they have the highest evasion, and defense is equal to level. In my experience, after around 30-40 defense, very little hits for more than 1 point of damage. Now, a fighter with dragon armor, aegis shield, etc is around 65-70 defense, and will never get better. A monk caps out at 50, or 99 on easy play mode.
As for attack, monks attack is double their level. A fighter/knights attack, with masamune will never get much higher than 100, not even that high on normal mode (with level 50 cap). A monks attack is 100 at level 50, or 198 at level 99. Now add to this, that the monk has higher accuracy than a knight with masamune (more hits, therefore more damage) multiplied by the fact that monks get 2 attacks per 32 points of accuracy, rather than 1... and you get THOUSANDS more damage. By the time my knight was regularly getting 1000 damage hits, my monk was landing hits for well over 10,000. No other job fighter, mage, or anything else can do that. And for free...
Which leads me to healing. More than enough money laying around to keep 99 heal potions. Using four monks, I have never run out of heal potions in a dungeon. Using fighters and mages, I have run out of healing many times. Not enough money top keep stocked on potions, and not enough spell slots to last through a long dungeon.
Really, if you aren't getting good results from a monk, you are either equipping him with armor and or weapons (which i usually stop doing around level 10), or, you are just not spending any time leveling. I guess if you are going for the "I beat the game with the lowest level" award, thats fine, but I find that the sense of reward that comes with leveling characters up is one of the main reasons I play RPGs.
PS my last completed game save file: Knight 67, Monk 99, Ninja 65, White Wizard 65. Note how my monk died the LEAST...