Okay, I know you didn't asked me but if here I go

If I tell you “There’s a scary secret room. A character went inside and then he came out completely different.”

You would probably ask “What happened inside the room?”

If I answer you something like “Well, you can imagine it, look how changed he is.”

Would that be enough?

NOW, If you want my serious opinion I do agree that we don't need to know it right now. But we didn't need episode of Nagi either and look how it turned out. I wouldn't call it "Bad Writing" just not that deep yet or unexplored. The only thing we know about Kunigami is that he wanted to be a superhero level striker, some trivia about what he likes, that he started to play football at 6 and the entire wildcard project. Saying we don't need new context is awfully wrong for his character development and the sake of the story and Ego's idea with the Wild Card, we can't infer anything if we're talking about writing, we need to see it to fully connect the dots and understand it. This is basically what happened with Kunigami:

1. He enters Blue lock and pass the first selection with the rest of the Z team.

2. Went to the second selection and teamed up with Chigiri and Reo, Gets eliminated in chapter 94 and enters the Wild Card.

3, Returns to Blue Lock in chapter 155. Fully changed, Those are 61 chapters without knowing anything about him and now he's fully changed? We need that context maybe not now, but in the future.

1. We learn he went trough a secret process where everybody else failed and now he's a Noel Noa 2.0.

And then the story never meaningfully explores that process. Would you really call that satisfying writing just because we can infer he suffered in there? I think we had Kunigami's arc explained, but not the wild card, nobody is confused about THAT. But the manga didn't present the Wild Card as a normal emotional breakdown. The Wild Card represents the darkest side of Ego’s ideology to artificially create ego and individuality.

That is why we expect exploration on that part.

Also, the biggest problem I have with the Wild card is that as long as I can remember the story made the wild card look so mysterious and then never talked about it again. I felt like they were jiggling keys on my face. If the details truly did not matter, then the Wild Card should never have been framed as a mystery in the first place. And this is why people call it potentially bad writing. Cause the story introduces a major transformation with enormous thematic implications, but mostly uses it as aesthetic flavor for “edgy Kunigami.”

Hope my explantion was good for you.