Everyone says you have to chop spidertron's legs, but I can easily just jump up and slice/whack his face off? Am I missing something?

I think Spidertron should be immune to attacks on his head until you destroy the legs. Becuase the 5000 one is easily killed by a simple sword swipe, or arrow, or hammer. And the 6000 one can be killed just by shooting his eyes, and is only a challenge in melee runs.