This story had no chance, and was garbage from the very start. Firstly, it’s established very early on that this guy was a “bait slave” for three years, acting as bait in low threat dungeons. But now all of a sudden that he transmigrates into the past he’s a fucking powerhouse. This doesn’t make any sense. There is no “hazing period” for this guy to regain any of his strength. He’s a nobody slave. Also how did this guy survive this experience in the past? The gate in the intro (where everyone dies) isn’t a “low threat gate”. On top of that it’s an unexplored one. Even if the MC did have knowledge from the future about this particular gate, surely these monsters would be able to find and then run down a feeble, weak slave. They aren’t exactly feeding these slaves top of the line grub. They’re expendable after all. But no this guy is able to dispatch all these fucking monsters with limitless magical talent & physical brute force.
I imagine there are more scenarios like this. If you use your brain to question any of the story threads it all collapses. Save your self the time and don’t read this.