I pay close attention to the managerial aspects of hockey, and so I get a pretty good idea of where talent comes from. Most of NHL's talent comes out of the draft, and about a third of it comes from the deeper parts of the draft where it's anyone's guess as to who emerges as an all star. But some part of the talent system is not just hoping for good luck in the draft, but making your good luck in the draft, when you had a team like the Red Wings and the Predators developing players properly and becoming a threat because they were not the kinds of teams who could flourish in free agency.

In league, you're not "making your good luck" without a sister team. Talent you get from challenger or masters is unrefined, and they have an x factor: how good will this player be in a team environment and as a professional? You can be the best player in the world at soloQ but only be an average pro because your integration into team environments is lacking. However, this can be developed, especially if you have sister teams where you apply a system and those players are psychologically adjusted for the rigours of a pro-team environment.

I would say that yes, sister teams are absolutely necessary, and if you do not take your development system seriously, you're going to find that other teams will turn average players into excellent pros while you have to buy excellent pros who only become average players in your system.