Until further explanation, no one currently in the verse can defeat Gapryong Kim.
PTJ completely broke Lookism's power scaling with Gapryong Kim.
He introduced various high tier abilities, but the execution of the "Conviction" ability ruins the balance. The concept of Conviction isn't bad on its own, but the way PTJ writes it (especially in this arc) essentially boils down to: "If you're stronger than me, I'll just overcome my limits and become stronger than you."
If the current top tiers are supposedly stronger than him, why wouldn't he just overcome them too? He possesses unmatched innate strength, and his Conviction punches only hit harder as the fight goes on.
That's why post-Shingen fight Gapryong isn't functionally any different from his earlier versions.
All he did against Shingen was fight him and overcome his strength. So why wouldn't he be able to do that against anyone in this era?
In my opinion, this writing mechanic feels like a complete asspull. But a lot of fans aren't ready to have this bitter conversation especially when it involves their favorite character.