Re: Natsu Dragneel
I too subscribe to the theory that the Dragons are within their students. If you read the chapter (101) over, it just seems to make plain sense. You look at the dialogue and Grandine says she felt that Igneel was close by, but it's obvious Igneel isn't wandering. It would seem that for some reason, the Dragons have had to withdraw from the world, though the reason is what? I also think that it has something to do with Zeref? Is it possible that he's a dragon too? I'm also of the opinion that Gérard is a Dragon Slayer.
That said, Natsu is sheerly frustrating. He's been shown to be one of the strongest in Fairy Tail on several occasion, perhaps only bettered by the likes of Makarov. However, all of his power ups are only temporary. How is it that Ganjeel for example is an S-Class level mage and yet Natsu isn't? We're all forgetting that Natsu beat Luxus and has beat many of the enemies that have bettered Fairy Tail but the author seems to keep on coming back to this idea that Natsu only done it via a cheap temporary power up or through his power of friendship and using those same excuses for over 150 chapters is nothing short of boring. I also object to the fact that Natsu's temperament and maturity are being kept at that of a five year old in order to facilitate the gags of the manga.
The fact of the matter is, Gray is a cool character but he should be at least a tier below Natsu now. But it won't happen because it's handy for the gags that they're equal. How the fuck Ice Magic is supposed to be at the same strength as Dragon Slayer magic is beyond me, but whatever. Natsu should be on par with Elza (using the spelling that Mashima romanised in-story) right now at least, though I feel he should've bettered her by now. That said, I do think that Lucy should be keeping pace Natsu. Her strength should be visibly growing as she accumulates gold keys and the strength of her Stellar Spirits should be growing along with her. There should be an arc in the making where she'll be forced to up her own combat skills in order to better support her Spirits but I doubt that will happen because it's not very gag-useful to have her being strong and dependable.
All in all, when you look at this manga, it took the art work of One Piece, the fundamental principles of the story, upped the gag factor and kinda shot itself in the foot at that point. I'm sure that while Mashima is enjoying the merchandising money that he's undoubtedly raking in right now. And yes it's blatantly a motivating factor given the introduction of Charle. He has no intention of turning this into a great manga, merely a fun one for the kids that seems to want to actually not want to go anywhere. Congratulations to him, selling out your own manga is fun!