@zanonyn
First, "necessary" is not the same as "overconfident".
MCs problem is that he assumes that he can take over the planet all by himself. That is definition of overconfident. Even with technological difference.
That would be fun. Magical fantasy worlds have gods which are nigh omnipotent. And after MS assuming "ha, their world is primitive, I can take over", encountering a nigh omnipotent entity which effortlessly defeats the MC would be a good slap in the face and a nice reversal of the overused trope.
The issues here is that when technology and magic clash, it is common for people to assume that technology would win. And that's where those series are currently going.
However, a civilization with magic can go in its own unique direction which will be unlike that of a technological civilization, and would still be as powerful if not more.
For example, at the extreme case you could have a supreme being which has long transcended humanity (or whatever it was oriignally), and for example, is one million years old and spent most of its life researching the secrets of universe. For all practical purposes, it would be all-powerful. Such entity is more plausible in a magical world, as those more readily provide means to achieve immortality, or transcend limits of their species. Unlike technological universes.
So a clash with something like THAT could be extremely interesting. Sadly, it is much more likely that from here on the manga will head in direction of MC roflstomping every empire on the planet.