I just looked at today’s schedule and they both have the exact same, 117 flights each. SAN is maxed out due to gate availability but STL can still expand with plenty of gate space available/unused. I have heard for a couple of years now that they want to take some of the connecting traffic out of MDW and funnel it through STL to reduce the congestion in MDW. Not saying STL will grow to be anywhere near the size that MDW is or that it will be the next base but there is potential there.