The whole point of pre-clearance in the VRA is that for a century after the civil war, every time a court bothered to look at some obviously rigged scheme to avoid compliance with the 15th amendment and knocked it out, the relevant jurisdictions would simply come up with some other way to reduce black voting.

After a while, they even started repeating plans that had been knocked out decades earlier.

Pre-clearance is the only known approach for dealing with this kind of obstinacy.