After some further thinking, I have come to realize that the "it's all Jack's dream" theory is the one and only completely coherent interpretation that's been proposed. Anything that doesn't seem to make sense or seems incredibly convoluted is thus easily explained, because dreams are typically nonsensical and convoluted. Often in our dreams, we are not even the protagonist, but rather a third-party observer; and sometimes we are not even ourselves. Certain things like numbers recur in inexplicable places. Nothing is what it seems. And when we dream, we usually don't realize that we're dreaming.
But while I concede that it's a totally valid and reasonable take, I find it to be monumentally unsatisfying. It's unsatisfying for pretty much the same reasons why "it's all a dream" stories are commonly considered to be unsatisfying. It's too "easy," and feels like a cheat. There's just a fundamentally nihilistic aspect that undercuts the emotional and intellectual engagement with the show. Nothing that we see on the show ultimately "matters." The mysteries don't matter because they aren't genuine mysteries. Caring about the characters becomes incredibly difficult if they're just figments within the protagonist's imagination. The conflicts don't matter because nothing real is at stake. The show cannot be enjoyed as a drama about people, their struggles, and their relationships. At most, it becomes a game of decoding symbols in a 121.5-hour-long psychoanalysis exercise. There are no great themes worthy of reflection or discussion. There's nothing significant or meaningful to take away from the viewing experience, other than a basic sense of entertainment. Does the show deserve to be reduced to that?