I'm with you on this PoP. I've never bought the 'break in the line' argument. When the jacket is closed the belt is invisible. If it's open then as you say there is already a very obvious break at the shirt/trousers boundary. A belt may serve to emphasise that if the colour stands out a lot from the trousers, but that's all. I prefer side adjusters, but if I don't wear a belt it's not to avoid breaking any line of the suit.