South Park used to be extremely strong in this tournament, and still is an upper carder, but has definitely fallen off from its prime (when it made the finals). Teen Titans has been at least a bit stronger than South Park for a while now, and while the margin of victory is surprising, I think this might've just been a bad match-up for South Park in general.
This signature won't change until Chrono Trigger gets a re-release on a modern Nintendo console.