Fire Man harder than Elec Man? Dive Man harder than Ring Man? Are you going by plasma or by weakness? Cause I can see how Dive man would be hard if you are using the skull weapon on him. He's actually easier to beat with plasma than with his weakness. His dive attack ing hurts which is why I don't get up close and personal with him.
I can agree with everything about Mega Man 3 though. Wily's second robot is very difficult. If you Rush Jet the mofo he's easy as cake, but if you go the hard knuckle then you're in for a challenge. If we're talking plasma then it would be safe to say that is the hardest Wily robot to beat outside of the skull capsule in MM7.