So, what is the difference between a publisher and a distributor?
I thought they are the same. I assume you don't need to make a demo. You can just make a completed song, upload to a distributor, it will be published on all platforms, done.
Also, is Songtradr anything special? Is it better than other mainstream distributors such as CD Baby, DistroKid, TuneCore, etc?
https://www.ascap.com/help/career-development/corner1 explains what a publisher is and does
https://www.liveabout.com/music-distribution-defined-2460499 explains music distribution
You ask in a reply if registering with ASCAP was triple dipping. No it's not. PROs collect your performance royalties and pay you for them. SOCAN in Canada does basically the same thing.