Well it's probably somewhere in the middle of the 0-25% range anyway.

I'm not sure this is really a decent way to think about ROI, as there's a lot it doesn't account for in that sense. It's more about psychology.

Now, I'm not advocating for you to join voting cabals, but truth be told they are the most profitable way of exchanging votes, ethics aside.

Fundamentally a cabal can only get you as much as a self-vote. You're just trading your vote for someone else's of the same size, and the result is the same. There are lots of better deals out there.