It's a mistake to attempt bald damage comparisons like this. Fighters usually do more damage over the adventuring day. Wizards will spike when the circumstances allow and may set up situations where the fighter does more damage. In my experience, if you only count damage that actually matters (i.e. ignoring damage that doesn't count because the enemy is already at zero hp), the paladin ends up top and the cleric bottom but there isn't as much in it as you think and a cleric with Firestorm in the right scenario will come out top if enough victims are close together.