Normally the medial underside of heel has no wear whatsoever. does this mean that i supinate or have mild varus feet? stability shoes r worse?

Heel: This means that at heel strike that you hit on the lateral side of your heel in a calcaneal varus or underpronated (supinated) position. What happens between heel strike and push off determines if you are a underpronator, neutral or overpronator. Underpronators usually have pes cavuum and should use cushion shoes or accommodative soft orthotic. Overpronators usually flat footed and need control.

Normal gait: In the normal gait cycle, heel strike occurs on the outside (lateral aspect) of the heel. As we the continue our gait, we shift the weight medially (to the inside of the foot) so we can propel off the big toe joint. As a result, the areas of the outer portion of the heel and the area below the bigtoe joint will show wear on the sole of the shoe.