I really enjoyed this novel and though I somewhat agree that the Mc letting his enemies go is a bit annoying, it's made up with how as you continue reading the plot is slowly tied together to become a whole which I thought was pretty good.
I always feel that when novels with protagonist's that have been reincarnated have childhood sweethearts and the protagonist acts completely oblivious to their feelings until "all of a sudden" they realize they are no longer that "little kid" and are all grown up that they have feeling for them as really weird and gross.
Why is he explaining so much knowledge that he isnt even supposed to know(Only having read at most two books) to someone he just met? It's like he's asking someone to become suspicious of his source information.