If seborrhea is oily flaky skin, is dry scalp dandruff then not seborrhea?

It is..mildest form. Dandruff is the mildest form of seborrheic dermatitis (seborrhea)...It is more oilly on face, thus you see the oily-flaky skin/scales... If otc products/shampoo not helpful, consult your doc for possible more effective treatments... Good luck.