Method acting is an interesting topic. I personally believe it is the most effective acting method, but a great actor needs to know how to turn it off.
A great method actor can become and experience life as the character without letting it affect their regular psyche. They can embody the character and actually experience the character's feelings, desires, and intentions. Of course, since it is real to them, it becomes real/convincing to the audience. But all of those are in a box inside their head, separate from their personal emotions.
I'm no genius, but I suspect that many people have a hard time separating their emotions and feelings. If they get angry in character, they might remain angry after dropping character.
Another issue with method acting is forcing yourself to take actions out of character. The characterization which you embody may not be willing to act a certain way, but you need to make them do it anyway. That reason could be because the script calls for it, the director calls for it, or the setting calls for it. Your character might not be the focus of the scene/story, so you need to act out of character to let other characters shine.
I personally would actually like us to have a different term to differentiate method acting. the method acting we see happening here in Oshi No Ko is what people usually think of with method acting. You overwrite yourself with the character and lose yourself in the process. You tie your own memories and experiences into the character and blur the line between self and character.
But there is another form of method acting. A method where you don't connect with the character. It's like imagination. You pretend yourself to be something you're not. You immerse yourself fully in the character and embody it, but not by pulling from your own similarities to the character. You embody the character while keeping them in a place of fiction within your mind.
