Countering Righteous Glory?

With strategy! Bring some disengage to your team comp, poke over walls or try to get the enemy low enough that engaging becomes risky even with RG.

RG active is only a speed boost, so using your void ooze slows them down effectively. Other than that, things like Azir ult, Anivia wall, Janna ult, or any other hard disengage is great for peeling a fast moving enemy team, just like whenever they have a Sivir or Karma.