system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] If Warp entities are created and fueled by belief/emotion, does that mean that human religious entities (God, Allah, Buddha, Jesus, as well Hindu, Greek and Norse gods etc.) would exist somewhere in the Warp? If so how powerful could they be?
gpt
None-extant.  
Just having people belief and feel something is not really enough for the Warp, you need quantity.  
And there quite simply are not that many humans around when those gods were worshiped. By the time human population become quite big (numbering in the billions), most worship was gone, and even then it probably would not produce anything more than a tiny spirit in the warp.

A third thing that one need to account is how close a species is to the warp. Eldar and Orks are close to the warp (in different ways) but humans was really not close to the warp until the later stages of the Dark age of Technology.

Look to the Tau, why is there not a "God" of the Greater Good? Because the Tau does not even blip on the warp.