Some Gameplay Questions

Does every creature eventually show up “in the wild” (so I can extract the core), or are some breedable only? God reward creatures can only be purchased from the god; I’ll never find them in the wild extractable or as wild eggs?

Does realm depth affect the quality/quantity of loot? (Assuming I’m not getting the penalty for being underleveled, do deeper realms give better loot/resources?) Or are achievements the only thing that matters?