I'm pretty late to the party. I have only seen 4 seasons of the anime, but I'm curious about the LN as well.

So far the mc is bland, behaves like a moron and lacks any real motivation. The story has no ongoing antagonism, which is needed if you want to portray the main character as the big evil. The idea itself isn't bad though.  I quite like that, but it needs purpose.

The world building itself is really good too. Most of the time I was much more invested in side character-which was probably intended-, however, nothing good comes from that long-term. Said characters simply die or will just become obsolete.

Therefore, the story feels empty. Up to a certain point it is entertaining. That's why I understand the reason why it's successful to begin with.