That logic doesn't always hold up. You could make tiny tiny alterations to some plastic container, put some random bump here or there, or make the flap stick out a little more, and the plastic container might suddenly not be usable due with a third party automatic coffee maker. That's a huge effect, despite the tiny change.
But I doubt that would make that case that because of that huge effect, those random bumps and extended flap deserve patents. We are after all talking about basic shapes here, nobody should be able to patent "a round shape with a tiny bump sticking out" so that others cannot use that shape.
I don't see how this addresses grandparent's comment: if it does not have increased efficacy, why are so many people desperate to use it? The amount of alteration is a separate issue.
But I doubt that would make that case that because of that huge effect, those random bumps and extended flap deserve patents. We are after all talking about basic shapes here, nobody should be able to patent "a round shape with a tiny bump sticking out" so that others cannot use that shape.