Just to reiterate what others have said: the monk numbers in the OP are completely wrong because the OP is not using martial arts and flurry of blows properly. Plus he's not using a quarterstaff, which is free damage with no downside.
So the monks should get two staff attacks for 1d8+5 each, and using flurry of blows, two unarmed attacks for 1d6+5 each. (One unarmed attack without flurry.) All at +8.
So that's 15.125 dpr normally, and 19.8 with flurry, against the fire giant.
But even that is highly misleading, because in one level the fighter gets a 50% boost in dpr.
Plus, the survival numbers are just silly. Yes, if a monk stands still and lets the giant hit him in the face he'll die quickly. But the whole class is designed around mobility and disabling enemies.