The inequality is not the root for why they are arguing that we should stop using "dyslexia" but because it they say dyslexia outright doesn't exist.

The inequality issue is that a spurious classification of children that gives access to better resources but is only available to parents that have the time/money/influence to get a diagnosis for their kids. The point is that having a incorrect label is not just a harmless historical idea but something that we should be motivated to eliminate in favor of a more truthful (and equitable) system.