Do Steem Witness proxy votes automatically set up a proxy for the SPS system? That is something I hadn't realised and seems to be what is going on here. I have some secondary accounts that already point to my main one and didn't realise their existing witness proxy votes feed through to the SPS system.

Yes. I tried to explain that in the post. You can only have one proxy and that proxy will both be able to vote for witnesses and proposals on your behalf.

I accept your point of view on the @jpbliberty case, as we go along perhaps we'll change some hearts and minds on how transformative this could be for both Steem and the rest of the crypto and Web 3.0 world.

I'm always open to having my mind changed and this is for sure nothing personal. I wish you all the best on that road!