You'll find a lot of clubs have a lot of players not turning 18 this year, Magic for example have quite a few U16 players permanently in their U18s. Some clubs may have majority 18s at least for one year but the next it won't be. Most will be affected.
Furthermore U18s end of youth, the point is also about developing your players, which is why it is a club championship. Build your players up, if your 18s aren't going well because you've developed them poorly than the club needs to look at themselves and their program rather than just blaming the players.
If you took U18s out and said now it is U16s, then your argument about one team primarily made of players not involved next year would actually be a lot stronger because the vast majority would be aging out the following year.
Some clubs certainly do play their weaker U18s in reserves when needed over the stronger ones. Something players should keep an eye on and decide if they want to play U18s or if they want to be challenged and go to a team that will still give them reserves time.Also would be interesting to know how clubs prioritise reserve grade vs u18s in the current format. Theres an argument that Reserve grade is the least important team in each club as it doesnt affect pro/rel at all. Does that mean clubs are more inclined to keep players in u18s and earn points instead of promoting them to ressies?






