Nice post, Airfix. I worked for a major bizjet manufacturer as an engineer for several years in a junior role and I concur with everything you say about the nature of that kind of work. I left only because of layoffs. It was rewarding having an effect on new airplanes. I generally enjoyed the work although it was very dull at times. At the junior level, engineering work is strongly team-oriented, so you do not have sole ownership of very much of what you produce or come up with. Your work is checked and rechecked by others so many times that you will be at best a team player in a team effort. That can be fun as well, and I produced many ideas that found play in the final version. But in the end it is not a very personal job and little of what you do is identifiable as yours. You have to identify with the company and the product.
I then took a fulltime flying job mostly to build flight time for use in subsequent engineering work. I agree with your thoughts there too. There are quite a few aero and mechanical engineers working as pilots where I work, even being a small company. They left the office mainly because they wanted to fly more and have more time off. But the pay is very low, far lower than even entry-level engineering, and I find that it saps my self-esteem to be making so little with my background. If you decide to fly fulltime be aware that your self-esteem may come partly from being well-paid, and when you get into flying you will have less than half of that. It is particularly hard for formerly well-paid persons to make the switch. In flying we take half of our pay in landings, takeoffs, adventure, and travel.
Both jobs are great in some ways and I value both experiences. Perhaps the best solution is to alternate between them, valuing each for what it does.