Granted he bypassed Demon kings magic with his darkness which zeldris could not believed he could do.
And what about this makes Mel above King when it comes to magic? Just because he bypassed the DK's magic doesn't mean he is above him in that area, specially when the portrayal in the series states otherwise. Mel has always been a pure physical fighter, his magical state has been very low compared to his strength (not taking into account OG magic). On the other side, King has always been a magical power house since the first chapter he was introduced (he has 0 strength and his spirit is not that high).
King's Chastiefol allows him to do multiple kinds of things. Can launch attacks that have an extreme destructive capacity (Spirit Spear Chastiefol, Sunflower); can summon a giant guardian that can be used as a means of both defence and offence (Guardian), can petrify people even if they're immortals (Fossilization), can heal (Pollen Garden) and there's more. Not to mention that King's innate magic Disaster allows the tiniest scratch to become a mortal injury.
Mel's magical feats, as much as I like him, pale in comparison to King's versatility, unless you're taking into account his OG magic (which clearly isn't taken into account given the context of this versus). He only has FC and darkness attacks (which include the attack with the dark clothing he did to Zeldris).
Plus, if you look at it closely Mel's feat is inconsistent asf. His darkness was able to overpower the DK's magic but still Estarossa (60.000) was able to resist that attack better than Zeldris. Not only that, but we don't even know if that attack Mel used was magic or not (it has been showed that PoD can be used when you have zero magic as showed when the commandments flew without having any magic due to the seal). In my eyes, he used his clothing of darkness to crush both of them.
King's feats on the other side are pretty consistent. His last feat shows without any kind of doubt that he was able to fodderize someone who was 200.000+ and most likely had most of his general stat being magic (after all, he didn't show any kind of physical feat, only magic attacks).
Even if you want to go with numbers, it doesn't make any sense. King has to have a magical stat between 200.000-250.000 (which is pretty much all of his overall number). If Mel had more magic than him as you state:
Strength: 120.000+ (probably way more, just lowballing)
Magic: 200.000-250.000+
Spirit: Dunno, let's say between 5000 and 10.000
You don't need to be a genious to see that he would be almost 400.000, which doesn't make any sense. As I said, just because he managed to overpower a nerfed version of The Ruler with an attack that we don't even know if it was magic to begin with doesn't put him above King, specially given the inconsistency of the feat and the portrayal of both characters during the series.