It's true. Any car cover will generate minor swirling and webbing in the clear, no matter how soft it is. Contaminates from driving the car still exist betwen the cover and the paint, and that is what will act as an abrasive, not the cover material itself.

What a cover will do though is improve the longevity of the interior. So for many people, it's worth it to have to do a fine polish every month or so to remove the swirling in exchange for having an interior that doesn't fade from sun exposure.