I can't speak for everyone but I think most people feel like this. I'm not old enough or experienced enough to tell you if you should rattle the cage or stay the course. I've been wondering a lot myself if I'll be in your same shoes 5, 10, or 20 years from now, since I've officially begun life as a professional. I was sure this was the direction I wanted to go but now I'm wondering if I'm going to feel fulfilled where I am, or if I should have tried pursuing something bolder and more punishing like academia. I felt very weary and disenchanted with it as a student though. I once saw a professor talking in a candid setting for a roast in his honor, for his distinguished contributions. He said it was strange to him to be recognized by the group since he considered himself a failure. He talked about how his career had been marked by a succession of disappointments. So I'll watch this post and the replies eagerly. I don't know if any of this helps you, but I think you're not alone.
That's interesting what you say about the professor. A good friend of mine turned down academia after becoming disillusioned of it's tribal/in-out group/club-ness, yet still wished she had accepted at other times. That's one of the frustrating things about life, you only get one and every door entered is a multitude of doors closed.