The main issues with this manga is that it has no clear direction. The author intervenes whenever necessary and assumes that the reader will just follow suit. It started really good with him getting his new power but the chapter after he got an OP weapon. From that point on he just became ridiculously OP. That aside he had no goals if not serving the fl. Problem is we only saw like 2 interactions of them so for the mc to be totally infatuated with her make absolutely no sense. He now wants to devote his life protecting her like what? Before meeting her didn't he have any goals he wanted to accomplish?
As if it wasn't enough the author shove into our throat the whole deadly sins plot. All of that mc is just following whatever comes in front of him without a clear goal. This is not how you write adventuring stories. Mindless killing for the sake of it. And all of the stats are broken, you see monsters with 100 millions stats point but it doesn't seem like that country has so much manpower, it should have been destroyed already. Coming back to the sins stuff. Advice for authors, don't write stories where you have some kind of big conspiracy with someone controlling everything from the side. It removes any sense of importance and lower the value of it all. Now someone new the mc had power and observed him and basically chose his fate, that means that he doesn't control anything in the story. And that makes your mc weak. rant over.