I agree on that effect, I left out various complications. A flip side to that would be the number of cortex neurons (and equivalents). These decrease rapidly in simpler nervous systems.

We don't object nearly as much to our own pains that we are not conscious of and don't notice or know about, so weighting by consciousness of pain, rather than pain/nociception itself, is a possibility ( I think that Brian Tomasik is into this).