I want to nerf them because they are OP, which in particular causes the Romuva to disapper in a few decades.So you want to nerf the Norse because one pagan religion is too weak to fight everyone else? How does that make sense? It's not just the Norse wiping them out.
Norse can farm gold and prestige like nobody else, blocking CB on eastern Europe won't make them really weaker - if you play as one of them you can still conquer the world and the pagans too (claims from concubine). Let's just make it very hard for AI due to historical reasons, shall we?
If you seriously think they don't deserve a nerf, look at this: