Whats there not to understand?
It is successful because it
- has definitive character designs
- has crisp fresh modern artwork
- disrupts the fantasy genre by turning it on its head with a unique and gamechanging magick system
- innovates by not having a typical cold blooded heartless rival filled with evil revenge thoughts
- has masterful writing that streamlines storytelling by not focusing on pointless tangents that no one will care about ten chapters from now
- has human and ever changing characters that are lovable and easy to embrace
- has action that doesnt feel devoid of life and meaning
- is an original story comparable to a Tolkien masterpiece
Well, I disagree about most of your arguments-
1. Well, is has its own artstyle, which also works with the characters. I guess, it is one of its strengths.
2. I dont really know, what 'crisp fresh modern artwork' means. I admit, I do like the art of the zombies, for example. If Tabata wants to draw something dark, it does look good.
3. Hahahaha... no. It's just a generic magic system, with the elements as its core. If you really want to read a game-changing magic system, when I recommend you to read 'Mistborn'. Allomancy actual is a game-changing magic system.
4. Well, this isnt that difficult, when everyone declares that they want to be Astas rival. It's impossible to describe them all with just one trope.
5. And yet we still got the whole gluttony-sequence of the cotton-mage.
6. Well, the witch and the necromancer are extremelly one-dimensional(& cliche). There are characters I do like, like Fuego Leon & Noelle, but that is still a far-fetched description.
7. Nothing really special.
8. We got 'the underdog wants to be the best of all'-story. That, and all the accusations to be too much like to Naruto/Fairy Tail arent very helpful, either. Admittedly I didnt read the Lord of the Rings books(just The Hobbit).
I dont want to say it's bad. It is just... OK. If it would be bad, then it would be cancelled already. And although most of its originally hate was very exaggerated, you could still see, where it came from. I still read it(I really like the artstyle), because I like Noelle, but until now, it wasnt really memorable.