source: I'm a terrible amateur welder
My conception was that we're adding power by increasing the voltage and we're stacking up material by adding wire, so to get good penetration on thick material I want lots of voltage and not much wire feed.
But actually it turns out that you make it hotter by increasing the wire feed speed.
I don't really see why, but at least now I know.
Here's a more recent weld: https://img.incoherency.co.uk/6464 - still not great but not nearly as bad.
I'm learning with you.. the polarity was fresh in my mind because I recently got half way through a project with little bb's splattering everywhere before a friend with more knowledge asked if I had recently changed wire.
Welding seems to be a lot like baking; It is very deterministic in a sealed environment and the parameters are well understood, but in practice the experts rely heavily on feel and experience more akin to an artist.
Love the spirit of the build, though, and it's a case where weld cleanliness doesn't really matter, so, more power to him.