I thought Nakaba said Arthur is going to surpass every Sins.Arthur's magic power should be something that enables him to fight on par with people who are massively superior to him in Power Level. Right now he's 40k, even with Excalibur's power he couldn't deal any real damage to highest ranked demons. His current half-dead state is probably going to awaken his dormant power, but even so I don't see him reaching 100k, much less AM Meliodas' 142k.