Yes I agree.
I do think though there must be some benefit in muscle memory from having to perfect all those basic skills as well as the extra conditioning but I don't think it outweighs the benefits of moving on and gaining skills. I think so many kids must lose interest, most of the clubs around here don't do any uptraining, just train the level you are on, then at the end of the season start training the next seasons skills. so therefore no chance of skipping levels, no chance of learning something exciting in the areas you are good in, and the added issue of kids learning the harder moves once they've lost that invincibility of childhood, and also for the coaches the much harder job of spotting much larger heavier girls.
I know the American system would have suited 2 out of 3 of my kids, the youngest one less so as she is the graceful one.
Without the push of college gymnastics, high school gymnastics, scholarships, olympic hopes etc it's no wonder we have very few higher level ndp gymnasts, they haven't gotten far enough before the other teenage interests kick in because they've been faffing around in levels 1-4 for 5-6 years.
And if there was more pushing skillwise at the lower ndp levels (and chances to skip levels if able to) I believe that more could test into idp later (as really it is a lottery of where you train and if you have the knowledge or proximity to an idp club as to whether you even have the chance to follow that path, never mind having to choose at 5 that that is what you want to do). Yes the skill set is different but it's not unheard of at idp 6 or so, and if there were more younger ndp gymnasts pushed to learn higher skills then I think many more could crossover.
And you are so right, the issue is yes you can compete those levels at far less hours but in Australia you can't 'compete' as everyone else is doing so much more.
I believe in the US also top 50% also get awards usually in the lower levels. Whilst often in senior age divisions here everyone gets awarded, lol, in the main, intermediate age group it's a small percent.
But at the same time I think physically it's better for the young gymnasts, some of the skills seem to be thrown by the young kids, most 4 year olds just can't do a good safe bhs - physiologically their heads are too heavy, their arms aren't strong enough, not enough back flexibility and they don't have the maturity to do these skills safely (ie not continually pushing for the skill if it's going badly)