Stories like this where the MC has hit kill abilities are the worst type. And its easy to figure out whats happening next. Bet hes finding a girl or a monster that he can tame in the next 2-3 chapters, or/and hes grinding to level 1000 or even higher. Just because its a RPG does not mean the MC needs to one hit every single entity. MC has no personality as well, "because its a revenge isekai" sounds like one of the possible answers for that. Until now, everything the MC has said or thought is in 2 categories:
1. I'll destroy this country, other rage stuff
2. Analyzing and questioning everything, including how to defeat monsters (that he can hit kill)
RPG isekai is becoming a "do not read" sign.