The way to level fastest should always be to do every dungeon once for the quests and level in the world otherwise. You shouldn't be spamming random dungeons and repeating them over and over and over. And to be fair I think even before these nerfs the random dungeon exp wasn't worthwhile after doing a few (once the risk of repeating dungeons has risen to a significant level). Regardless, it'd be nice if they buffed the exp for doing it the intended method, it's a little on the slow side. But I don't think it's that bad.