HRE vassal swarm is hilarious. I remember I got pretty lazy near the end, and just started making Client States and calling them "Iberia", "France", "Anatolia", etc and just feeding them entire cultural regions. So long as their capital is able to be added into the HRE, they'll be good to go and have almost no LD, and once the Age of Revolutions rolls around, nobody will have LD between that Age buff and Austria's ridiculous Dip Rep; I think I had something like 17 Dip Rep by the end. I didn't do Greyskin until the very end, but I don't imagine it being worth it before that (if you're going for the achievement).