Bingo! Just taking out the character being spoken to works precisely the same in any context and involves utterly no insight. Taking out Garfield's "dialogue" actually exposes the strips own canonical reality since no ever "hears" Garfield. It makes us focus on Jon's reality in a way which emphasizes the text instead…

I'm not sure it highlights Jon's insanity so much as his crushing loneliness. That's why I've always found "Silent Garfield" the far more interesting remix of Garfield. Taking Garfield out is ultimately just a cheap gimmick that relies on belittling mental illness for "humor". That's not funny, its just kicking people…