Recently my brother and I have been trying to get seraph crystals by killing the invincible bosses. I have killed Pyro Pete twice and my brother has recently killed Hyperious. On all 3 occasions, neither boss dropped any legendary guns (not that big of a deal), none of them dropped any seraph crystals, and none of them even dropped any loot worth picking up. For raid bosses, I thought they would drop way better loot, especially seraph crystals. How are you supposed to get enough seraph crystals for a weapon if the invincible bosses are not dropping any?
Edit: We are only in normal mode right now.