Notice how I didn't say that I "learned" both in a day, I "remembered" them. Of course actual learning will take some time, especially with less used characters. But remembering shapes and differentiating between them using mnemonics should not be too hard for most people.

If you want to learn pronunciation you should be listening to audio.

Sure, maybe don’t force people to learn kana first. But Hepburn is kind of the worst of all worlds, it is just a waste of time to learn Hepburn.