I would think most engineers used by eng. co.s are moonlighting or on retainer or family member. OS, Lee,Fox and all the others no matter the background, wanted to make small engines and that is where they put their talents, and except for maybe Jett or Laser engines, everything is copies of 20+year old designs; nothing new under the sun. Most new modelers are not interested in the mechanics of something which is why they can have such a hard time; a big boost for electric, and only in the last decade has the hobby become a consumer hobby.

Most machinists are very good self taught engineers as they are the first to know if the design is stretching too far the materials used; they are the first line of defense to tell the engineers if there might be a problem. The only ones who make things happen, though no matter the background, are the curious.