I always wonder if dark matter isn't simply made of wrinkles in space-time that just don't go back to flat after some weird event happens
While we don't know the details of dark matter, we do know a lot of things about it. Putative explanations have to cover a lot of ground.
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.
Far too many people get hung up on the idea that in science what things "are" matters: because it doesn't. What matters is predictive power for future observations - if whatever you're proposing doesn't predict anything different to "invisible matter" then it's exactly as bad an explanation as "invisible matter" which so far is a perfectly good explanation for current observations.
The universe has no requirement to satisfy the day-to-day intuitions of African-plains originated upright apes, with senses optimized to spot large predators, in how it works. Quantum mechanics is a great example of that.