>novel way too long and always the same thing
Sounds like a generalized opinion of long running series from someone who obviously hasn't read the source.
The only volume that ever felt like a filler was Volume 7 and this is after having read through all currently 20 published volumes. Each volume does great character building, albeit slow, since the passing of time itself through the volumes aren't that fast.
You can't even compare the manga and LN, the latter wins no question. It has better art, pacing and the jokes and references aren't butchered. Though the references get butchered in translation even more because no effort was made to even include them.
The way I see it, the manga ended before the LN because of plain disinterest in it.