Honestly, idk how I've ever felt about the ML but what I can say for sure is that both he and the MC feel very real. Losing people you care about is one of the absolute worst things people can go through, and there's a lot of shit in this world. I feel as if this author personally understands what grief feels like, people who haven't lost anybody dear to them do not understand what it's like to mourn the loss of a loved one. Your whole life you'll be mourning that person, thinking about what-if's and either trying to come to terms with their death or trying to preoccupy your mind.
What the ML needs to understand is that even if the MC IS who he wants him to be, life experiences change people. Whether it's through time travelling, reincarnation, losing memories if he is who the ML thinks he is 100% they're still two different people in theory. Each part of the MC has gone through different trials and tribulations in life, both have obviously suffered and are trying to do right by themselves or those they care about. Our MC is taking care of ghosts and facing things head on, but he's suffering at the same time.
I feel like golden eyed black haired dude has done something. He said no matter how vile, every soul goes through reincarnation and it's disgusting or some shit. He probably did something sketchy with MC's soul. Maybe in order to obtain him in one way or another. That could be why the MC of the past or whatever he is sealed the ML away.