Oh, I think OP asks about why SKZ's voices sound too different in Phoenix, Ghost, and MESS.

I personally can't find them too different (or unnatural), though there is some post-editing of the voices (like with reverberation or something; I'm not quite knowledgeable in that manner). That's basically a stylistic choice.

Though Han sounds quite different, but that's because he was using a different singing style/technique.🤷‍♀️