Where are you getting that percentage from? Regardless, the percentage doesn't really matter since the population size (especially greater metro area) between Houston and San Antonio is much greater. 1% EV adoption in Houston might equate to 10,000 EVs while 1% EV adoption in San Antonio might equate to just 1000 EVs. And 1% EV adoption in Poteet, TX might only equate to 1 EV. And obviously you do not need 10 superchargers in Poteet, TX just because Houston also has 10 superchargers.
With that said, SA can still use at least a couple more superchargers especially closer to downtown to help serve all of the visitors coming from outside SA. Right now, those visitors all basically go to the Huebner Oaks SC since that is the closest SC to downtown SA.