You've got a point, no doubt.
Anyway, to go into detail.
AP: Not a huge difference between the two, Akame is comparable to someone who one shotted a baseline and Natsu should be a bit Above that.
Abilities: Akame's OHKO sword is the perfect ability against Natsu, but Natsu has much better ranged attacks and can buff himself to get stronger if necessary.
Skill: Here's the huge isssue. Natsu, is a brawler, a fairly decent Brawler, but one nonetheless, he outclasses her range wise no question, but it's in character for him to go close in CQC, plus, he's super well known for being Hot Headed.
Akame on the other hand keeps her cool even in some of the most extreme situations, Her form only lasts so long, and she was fighting the General of the imperial army one on one and still managed to keep her cool and think her way around the situation.
Stamina: Wait this actually means something? ...Well....Yeah surprisingly.
Do bear in mind Akame is on a time limit, and that limit that lasts for one chapter, if Natsu keeps his range, he wins easily, and without much diff.
So. In conclusion, with her only needing one cut against the Salamamder, and her arguably being more skilled and keeping a much better head. Akame wins 7/10 times.