The animal welfare section is currently fairly sparse. If it gets fleshed out (no pun intended) significantly more, I could see it belonging as a top level cause area. It already has content about equal to the Specific Research and Improving Research, Decisions and Values sections, though of course those can grow too!

Right now Improving Research, Decisions and Values seems like it could get broken up into different sections, between Policy and X-risk mainly, but Improving Policy is such a heterogeneous group that I'm a bit wary of adding more to it...

For the (bonus) question on comparing impact of an "average" charity with the best one, it would probably be worth specifying whether we mean mean or median, as I know some people here expect (I think myself included) a very significant difference between mean and median.