That wouldn't be so weird as it sounds. From simulations we know that it was dark matter that came first, then came the galaxies. So if these wrinkles (they do

That wouldn't be so weird as it sounds. From simulations we know that it was dark matter that came first, then came the galaxies. So if these wrinkles (they don't have to be very smooth) simply had a (large) preferred size and clumped up faster than normal matter in the early universe, that would be enough. Neither of those would be particularly weird. When dark matter clumped up normal matter was essentially a very low density hydrogen cloud, devoid of stars, much less dense than a cloud in the sky, which would take (without dark matter) some 15-50 billion years to clump up by itself. As for the size of the dark matter structures, well we don't know what they are, so you can postulate any size for them.