User blog comment:Jopjopjop/Volume 19 Quotes / Spoilers/@comment-24098614-20141104025924/@comment-1359322-20141104134139

I'm not saying that Ishibumi has to show all myths nor has he shown all. I'm saying compared to Index, Ishibumi's hands is tied to myths only thus have limitation in story writing since Ishibumi has to take reference of what the myths is. For example, Ishibumi can't randomly create a God named Mondrax and say he's the Chief God of the Norse.

On the other hands, Index being a completely original story, in a completely different world, means the author can write all he wants and doesn't have to reference a thing. The author can say Mondrax is God or Devil etc. Of course i'm not saying Index is completely reference free, since the author uses church on the magic side and has use names like Lucifer and all, but compared to DxD, Index's flow of story is much free, thus making it extremely long.