Until very recently (as in the last 50 years or so), that's exactly what publisher meant. The people who owned the printing presses. The transition of publishers into pure selection/promotion/distribution businesses is fairly recent.

Yes and FB/Twitter != “the Internet” or even “social media.”

They happen to just own the largest scale implementation of that medium, much like a publishing house.

Except that certain things were illegal to publish, even in a country like the USA with its 1st Amendment rights. And some of the printing presses were fully utilized already, so your pamphlet about the true cost of capital concentration or QAnon wasn't about to get printed. And as for your screed against the owners of printing presses ... yep, you guessed it.