I don't understand why reserve teams often get talked about as some sort of panacea to various problems, when it's far from it. I certainly don't think that it should be mandatory - there are many ways to skin this particular cat and clubs should be allowed to do what they believe is the most effective thing for them.
Even when the reserves / alliance leagues were around, Leeds never really took them seriously, yet only the biggest of trolls could argue that Leeds haven't contributed their fair share to the game's talent pool in the SL era. The belief at the club has been and still is that it was better for young players to come out of the Academy team and serve their apprenticeship playing first team rugby (wherever that was), rather than playing fellow kids in the reserves. In the early days of Super League, Bramley were effectively Leeds' reserve team, and later on the club sent batches of players to London Broncos, Hunslet and Featherstone. In general, it has served the club well.
I think that's one reason why Leeds prefer dual registration and loans to a reserve team. I would argue that Mikolaj Oledzki would have learnt much more playing against men in the Championship / L1 at Bradford that he would have done playing fellow 21-year-olds in the reserves. Luke Briscoe's career seems to have been reinvigorated by his time at Featherstone. Brad Dwyer also earned his Leeds shirt back after impressing at Fev. Jordan Lilley needs to learn how to really marshall a team around a field, and I think he's better served doing that at Bradford or Featherstone. You get the idea.
I get the argument for reserves but in reality, clubs should be free to find the way to build the player development pathways that work for them. That said, there needs to be some form of monitoring in place to make sure that clubs don't just see the scrapping of reserves as a 'cost cutting' exercise. If you don't want to run a reserve team then fine, but you still need to demonstrate that you are developing players to elite level standard by whatever means you choose.