could a strong enough space player just shrink the red miles into something that's not a threat?

The Red Miles always have a source. Just take down the Source, not the Red Miles themselves. If they’re something like DD’s Red Miles on Derse it’d be easy to shrink them back. But if they’re Jack Noir’s on the Universe, it’s like. Spanning millions of light years. You’re not going to get them. Just get him.