Yeah, Tesla's per minute pricing structure ends up significantly under billing what I believe they really intended to charge because they don't have enough pricing tiers and because the over 60 kW price is effectively pegged to the bottom of the tier instead of the middle. This has only gotten more impactful as superchargers have gotten more powerful--first most V2s up to 150 kW then V3 with up to 250 kW. To have more "reasonable" pricing that more closely follows per kWh pricing they need tiers every 30 kW going up from 60 and to set the price to their nominal per kWh price adjusted for an assumed charging power of the mid-point of the tier during that minute. So, for example, if what they really want is to charge people $0.30/kWh for the charging session, then when they are in the 90-120kW tier they would price the per minute bill based on 105 kW charging during that minute--i.e. assume that a minute of charging in that tier actually delivers 1.75 kWh--and end up with a price of $0.525/minute in that tier.
But this obviously becomes quite unwieldy pretty quickly. The end result is that when Tesla changes from per minute to per kWh billing the effective price will always go up significantly because they were significantly under billing before.
