Yes, rules of cinematic narrative outweight the need to tell a faithful story. I.e. in Stargate universe it would be really boring if the Goa'uld just came, slaughtered everyone and take the rest prisoners for experiments within the first 5min-1hr.
Exept all humanoid life in the modern galaxy was the result of an Ancient experiment, when they seeded their genetic code through a wave traveling through the stargate network. I am not aware of any research on the topic, but I suspect that would scew the odds of humanoid civilizations being at a relativly equal level. Then, it could be argued, that the Goa'uld only get their technological advances from the host species, humans, so they cannot be that far beyond us.
