Todd Armstrong being dubbed

I heard once that Armstrong had no idea that his lines were dubbed over until he actually went and saw the movie in the theater. I also heard he had a lot of personal problems and his career unfortunately never took off because of (or perhaps adding to) them. Do you think there is any truth to this? I can imagine why a lot of actors would be shocked an angered about finding out their performance was dubbed over even if their voice is better. For the longest time, I had absolutely no idea he (or anyone else in the film) was dubbed over since the dubbing matches up so well. The Brits certainly do it better than Americans historically, along with Germany and Italy where it's sometimes hard to tell whether some roles are dubbed or not. In Italy pretty much every movie was dubbed up until the 1990's at least. I imagine it may have cost him some roles if he showed up to auditions with a different voice than people knew him from (the same thing happened to actor Michael Sopkiw when he tried to jump from Italian B-movies into Hollywood).

Also I wonder why most Ray Harryhausen leading men (such as Kerwin Matthews, Patrick Wayne, etc) never went on to do much. At the time, they were in this big fantasy/scifi film that would stand the test of time, but sadly not experience a big career afterward. I imagine it's because people went to see the stop-motion monsters and not the stars... or that there was kind of a stigma about taking a role in a movie that was deemed to be more "for kids" rather than adult audiences?