The number of threads and questions about slow Supercharging indicates that Tesla really needs to do something to #1 give the owner more information and #2 fix the outdated charger sharing.
Every Tesla sold in the last three years can charge at a very high rate to a relatively high state of charge that there just isn't much left for the second car on a paired stall. It was OK in the early days when the battery would peak only at very low SoC and then ramp down starting at just 20%. But today a 100 battery or Model 3 can charge to 70% at 90 kW or more. That leave the other car with just 1/3 or 1/4 of what they could.
The other thing is there are many factors that reduce charge rate. It would be very helpful to users if the car would give some info wht the charge rate is low. A cold battery, a hot battery, station at capacity, ambient temperature, ...