I agree with you, Superhuman is a pain to get. But for my experience in the second sea the hardest thing to get is either the core brain(if you don't have buddba) or ttk on public severs.
CDK isn't that hard if you know where the tushia torches are and how to do the CDK quest correctly(the only hard part is summoning the boss with hallow essence)
It doesn't have a requirement, u jus have to be in 2 nd sea and kill rip Indra and dough King and get mirror and resonant it. It's a pretty complicated process