My first question for you is whether you have had so-called mystical experiences. I have had thousands and I see the world in a way that most people do not. I say this only to make the point that I am not speaking from theory or the outside-looking-in. Unless you see the world in a certain way, which is wholeness, then the only way you can try to relate is through knowledge. And knowledge is but an empty reflection of the actuality.
I want to say here that we are not arguing. You always make intelligent points and well-formed arguments.
You said that realization may be subjective. Yes, of course it is. It can be nothing short of subjective, because it is out of this one expression with a brain and senses and body that awareness happens. What is universal or "one" is the essence that permeates and moves the body, brain, world, etc.
Next, you wrote, "I wonder whether there's a thin line, too, between realizing something and having only a hunch, intuition, or even prejudice that it's true." I used to think this was so and now I know, from my perspective that there is a major difference between a realization and intuition, prejudice, etc.. The latter are artifacts of thought, but the realization is beyond thought.
I'll leave it at this for now, but I humbly say that unless one has a so-called mystic realization then there is no way to grasp what it is without having it oneself. I think I explained this in the context of your skydiving analogy.