What are the celestial creatures the Conjure Celestial spell can summon?


Looking at the list of monsters, it seems that the Conjure Celestial spell really only act on three possible creatures:

  • Pegasus (CR 2)
  • Couatl (CR 4)
  • Unicorn (CR 5—requires spell slot 9)

Am I missing something? It seems very restrained for a spell level 7 to only be able to conjure 3 creatures…