This actually got REALLY boring after ch. 23~24.
The first "mass spawning" thing still had some new stuff going on, his party members learned new stuff and got new equipment and the whole demon thing was kinda fresh... Afterwards it is the same thing, always the same strategy, always the same skills, even the same enemies behind it all.
I seriously can't stand seeing him handing another piece of paper with a rune to Ruri.
I usually don't have a problem with op protagonists and all the generic shit that comes around with it, in fact i enjoyed it at first, but this is just too repetitive for me. I feel like i'm re-reading the same story with different monsters for the last 200 pages or so.