it sounds like you think that prep-op doesn't teach the same quality of skills that compulsory does. this is not true at all. Girls going through to level 7 either by compulsory or prep-op will have the same skills and mastery.
I believe that some may have the same technique, but I don't believe they will have the same skills, as they are trying to work with their strengths and weaknesses. My oldest dd had major fear issues with the backwalkover on beam, as well as clear hip issues, etc. She almost wasn't put on team because of not getting that kip. She got it literally the last week before they were allowed to compete. She was forced to work through these issues, not around them. She had to work over and over and over to get those required skills and work through it because it was required. I didn't think she'd make it to level 5, much less past level 6, truly. I really believe if she had been able to work around those skills and able to do something else, she wouldn't be where she is now. The gym she was at had high standards for allowing them to compete and it made her work hard to achieve those skills. Thus when she faced issues with backhandsprings and series on beam, yurchenkos, release moves, and double backs, etc. she knew there was no way out. Again, just my experience. I admit that I have high expectations of my kids, without being a psycho crazy gym parent, but I would like them to reach their potential if they have it and if THEY want it. I guess that's what I see wrong many times in today's society, as well as in gymnastics now. If it's too hard, we make it easier for kids, we don't expect them to rise to the challenge.