No, Feynman specifically said it takes a lot of effort and top quality understanding to explain stuff well enough for it to seem obvious to others. He didn't think it was automatic.
He further thought, for example, that being a good physicist takes a lot of imagination to come up with new and different ideas. In other words, physicists have to think of non-obvious stuff.
It's weird to assume someone who had lots of new and important ideas, and who put tons of effort into being a clear explainer of ideas, would be someone to just assume their ideas are obvious.
A sibling comment discusses people who don't do their homework before writing. I think people should not talk about public figures without doing their homework -- if you don't know what someone is about just stick to the topic instead of invoking his name.
Sometimes little tiny essays like this can be too vague if they use no examples at all. The examples are never the point, though, and it's assumed the example will just get translated in the reader's head into their own more personally-meaningful example.
But FWIW the Feynman interview that I was trying to find was his moment of seeing the spinning plate, which I think led to his Nobel prize-winning work. I couldn't find that interview, but I thought I remembered him saying that it seemed obvious at the time.
That kind of playful work - done for the fun of it after a long period of burn out - got him back on track for the work that eventually led to his Nobel. Interesting anecdote, but I don't think it's related to your thesis.
His motivation for not publishing all of it is hard to guess. You suspect it's b/c he didn't know that other people were ignorant of it, but he never stated that. My first guess is it's b/c it'd have been a lot of work to help others but not himself. When you have millions of great ideas, writing them all up for publication would be a huge chore and it's more fun to just work on more new ideas. Feynman cared a lot about fun.
Sure they do, if it's a thought in a chain of thoughts leading to something. People make mind maps all the time full of obvious ideas because it helps the find the non obvious ones. Hell people write down obvious stuff just to organize their thoughts.
Also, I do recall him stating that he hadn't considered publishing some stuff because he didn't realize it was original until someone else got credit for publishing it. I wish I had a reference, but I don't, I've read a ton of his stuff and couldn't pinpoint where I read it if I had to.