Firstly, you said we'd be using the 7-A versions
Rules: Speed equalized (for what it's worth). High 7-A version of both.
So I went with that. If not, then we can give Melodias casual country busting feats, which Natsu isn't topping. Especially considering this is about the same level as Etherion, and that took over an hour to prep. Even eat a single crystal with some of its power activated Dragon Force. That implies to me, that TOH Natsu, which was stated to be the one used in the bonus round, (unless ToH stands for something else, in which case please correct me), is weaker than the Etherion blast.
The best feat from someone around Natsu's level would be the lightning Laxus used against Ajeel: http://images.**********.net/mangas/fairy_tail/fairy_tail_447/fairy_tail_447_14.jpg?v5 which has been scaled to small island level:
https://vsbattles.fandom.com/wiki/Laxus_Dreyar
Assuming he's at that level at the current series, he's still no match for Melodias.
Also Melodias is truly immortal, beyond just his hearts:
§ Immortality Curse: It was revealed that the reason why Meliodas has been able to live for over 3000 years without any physical body change is because of this curse given to him by the Demon King. It allows him to resurrect if he is killed in battle, and practically stops his aging. However every time that he is killed, the Demon King will eat some part of his emotions, making Meliodas more ruthless than before, which will eventually turn him back into the demon that he once was.
https://vsbattles.fandom.com/wiki/Meliodas
But for sake of argument, I'll assume we aren't counting this, and that any form of death is considered a victory. In more recent arcs, Melodias has been able to access his demon powers without breaking free, ever since removing the binding placed on him by Merlin. Merlin stated that all Melodias was left with previously was 1% of his power, but I'll take that as hyperbole:
http://nanatsu-no-taizai.wikia.com/wiki/Merli
Suffice it to say, Melodias has also grown stronger, taking on both Derieri and Monspeet, very casually I might add:
http://nanatsu-no-taizai.wikia.com/wiki/Meliodas_vs._Derieri_%26_Monspeet
I feel that Natsu would rush in, probably with a Fire Dragon Iron Claw, cause he's a brawler by nature, but regardless, magic isn't helping. While Natsu is resistant to heat, differnet kinds of flames do take time to adjust to, as we saw with Zancrow. Also, with Melodias having a sword, it's not quite hand to hand, since he's got more skill, better range, and it's easier to deal killing blows, even if we assume the two of them have equal strength. Even if his clones are weaker than he is, more targets without magic is gonna slow Natsu down, and I doubt Natsu can survive a revenge counter.