This is a hard one, but on top of everything, I'm more inclined towards giving Legosi the advantage.
For the first part, AP gap isn't as large as the results of the calculations, as Legosi's punching wall feat it's not only rather casual, but also misses parts of the total fragmentation of the wall. Satan's feat it's around the top of his AP, as he was unable to break a 15th one. This is not meant to say that Legosi has an overall AP advantage, but to say that the gap isn't as big compared to the calculations done around it.
Regarding the combat ability, whereas the experience part definitely goes for Satan, Legosi, despite not being as competent in this area as he's currently, it's still a skillful fighter, being able to defeat 2 (Actually 3) characters stronger than him overall while outnumbered by 2 vs 10. So he isn't outright outclassed in this area.
That said, Legosi is the one with biggest brain here. He's smart enough to known when it's convenient to fight Satan directly or rather play defensive. He's also the one who has a general idea over how strong Satan can be as he's able to assess his stats and the one that, albeit likely unwilling to fight at first, the one who would take him seriously enough knowing what type of foe he's facing (and the fact that he doesn't tends to go casual on fights). Satan himself tends to make the mistake of being ruled by his ego while fighting characters he has no idea of their overall power.
Legosi also seems to have the stamina edge as well as always having the resort of his bite force, which is overall implied to be higher than his regular AP.
So, Legosi high-diffs.
TL;DR: I overall find them relatively equal on normal stats and skill but Legosi is the one who has the upper edge on smarts and stamina.