Doesn’t that depend on what you mean by ‘exist’? As far as I know, humans, angels, arch angels, demons, Lucifer, and Farmer (creator of this universe) are only visitors. Surely there must be other un-manifest beings (no physical or energetic form) of extreme power that cannot ‘appear’ but could easily wipe out the astral planes (or unexist them); this includes many over-souls. Additionally, for those that believe God is a being, God it is everywhere.
Note: since the energy is so dense here, visiting humans that take energy (or source it) are among the more powerful on the astral places where the energy is far less dense. That is why most of the beings on the lower planes are of no real danger to wandering humans in energetic form.