About the Yorick changes in 6.20
One of the changes is that his E no longer marks minions. This is actually a bit of a nerf to his split pushing. Instead of letting your mist walkers casually walk up to the enemy minions to attack you can just use E to make them jump to the minions. It might not seem like a big difference but considering that you can do this to every wave late game, the time adds up.
What i think riot should have done was to instead let the ghouls prioritize marked champions.