Population genetics tells us that selection is more efficient in larger populations. Consequently, and on average, species with larger efficient population sizes should have more of Useful Stuff and less of Not Usefull Stuff Which Has Even a Low Cost. This provides us with a simple test: how does the abundance of this stuff you are interested in correlate with population size?
For example, large population size species have less introns, shorter introns, less dead transposons, while small population size species (including the pinacle of creation) have lots of these things.
I rest my case.
(This idea is totally not original, but I can’t be bothered to look for a reference and I wanted to put it in writing for future reference for myself. Cheers.)