In the context of a Supercharger the critical metric would probably be cost per charge/discharge cycle for a given capacity bank. While a car probable averages

In the context of a Supercharger the critical metric would probably be cost per charge/discharge cycle for a given capacity bank. While a car probable averages a fraction of a charge cycle per day, a busy supercharger might be on the order 10 cycles per day. Super capacitors degrade more slowly than batteries with cycles. The use which might make sense is to use the capacitors to supplement the grid supplied power during the initial fast charge phase, then in the slower final charging phases or idle time recharge the capacitors from the grid for the next customer. This levels out the demands on the grid and can result in a lower electricity rate from the power company. It all depends on the constants if it makes sense. Or maybe it doesn't make sense and Tesla needed something out of Maxwell's patent portfolio.