My guess is "not very." Even in canon when Taylor was doing this with 5000+ parahumans, he wasn't giving a single fuck.
The key to Scion's strength is twofold: First, his real body is hidden in a shielded dimension. The Warrior and the Thinker separated the dimensions and walled them off before the cycle began in order to maximize results and ensure safety. Sting can breach this blockade, but anything else is useless.
Second, Scion is optimized towards fighting. All the best combat powers, nullifiers, precog, PtV (admittedly expensive, but not so much that he won't use it at all) and no limiters of any sort. Scion is capable of casually cracking landmasses and is exceptionally difficult to do any real harm to. On top of that, his powers are already plugged into each other the way that Pantheon is still learning how to perform.
There's two ways to beat Scion: Fight him hard enough to make him spam PtV and wear down his energy stores, which would probably result in most of the species being dead anyways; and get him to allow himself to be killed, which is what happened in canon, and required him to go on his rampage first, so that he'd be indulging his emotions and vulnerable to sudden swings.
No matter how advanced Pantheon gets, it doesn't change the fact that the Passengers themselves were hard-coded to be either harmless to the Entities or simple to defeat. I find it highly unlikely that any combination of powers could put Scion into a difficult position if he were to put any sort of effort into the fight. If everything else fails, he just triggers his unblocked PtV and wins.
