Ha.
That dead guy ended up being the usual MC of these reincarnator stories, then. That has a boost in power from having past memories and becomes OP.
I do enjoy when these guys, and the hero summoning ones, get a reality check.
I don't enjoy how it seems that most of them end up just going to the deep end when it happens. It is always like that. Even when it seems they will get a grip, the author makes them dive deeper into another trope.
It is even worse here since the dude just understood he is not the only reincarnator around.
Most of the time reincarnators at least have the excuse of thinking themselves special because they think they are the only one.
It would be nice if, after getting a reality check, the isekai'd/reincarnated person not the MC would instead get fixed up and use their powers properly to, next time they show up, make it clear they are a better person and become as good if not better than the MC thanks to the humbling.