Vader's pain is a joke compared to Darth Sion

That's the neat part: he isn't.

All that pain is to make sure the Dark Side is strong in him.

Bold of you to assume Anakin has ever been calm in his life…ever

Trust me, Vader is never calm. There’s an underlying hate to everything he does and everything that is.

He isn’t the suit is designed to be as unbearable as possible that way a constantly disgruntled Vader gains strength through pain