Hi AthrunZala,
Thank you for taking the time to give feedback. I emphasize that this is in no way a finished idea, but it was intented to share a concept for all those interested, in order to work out a way to realize the concept together. As I said I see multiple ways to realize the concept and I hope together we can figure out the best way to do so that tackles all concerns mentioned by you and others.
For example, I mentioned the possibility to work this out as a private league so it's optional (managers aren't forced to do something they don't like) and extra server capacity isn't needed too much.
As for the arguments:
1) While complexity is also a hurdle for new managers, having a U21 competition does get them to compete sooner. Because even without complexity, it takes more time to acquire money for or train top players than it does for U21 players. Of course, new managers need to figure out the complex game in order to be good even at the U21 level, but they can compete sooner.
2) Of course a whole test environment or faster trainer would be better for realizing new ideas, but as you mention that takes a lot more to implement. I think experimenting at the U21 level is helpful already, as it's a much smaller step than a full size experiment. My point is to shorter the experimentation cycle to get feedback faster, not necessarily a 100% representation of the real thing.
3) I think that if every country has a larger U21 player pool, differences will be smaller (benefit of more players is relatively bigger for smaller countries than for bigger countries that already have a large pool). Of course it won't fix everything, but I do think it's a positive. It still needs to be worked out practically but that's the point of this thread.
4) I don't think it will necessarily hurt the market. You focus on the increased supply, but there will also be increased demand by the teams that don't like to train but still want to compete (and thus increase demand without increasing supply). Also, I thought the current state is one with more demand than supply, so even if supply increases it would be a good thing.
5) Same as 2), I think with a small investment a relatively big benefit on this subject can be achieved. Experimenting on a small (U21) level gives a good idea already without the need of a seperate test envorionment for full sized experiments.
Don't worry, none of your comments are derogative!