It's nearly impossible to disentangle race and partisanship in the South, which is why this ruling could have such apocalyptic consequences for Black representation across the Deep South (more likely in '28 than '26).
Not a legal expert, but to my plain reading this is the passage in the ruling that seems most concerning for the future strength of Section 2, and likely why Elena Kagan was so alarmed in dissent.
The key question going forward: can plaintiffs produce evidence for any current Black-majority Southern district showing that racially polarized voting exists in a way that cannot simply be explained by party affiliation?