Billy Moore has made the Bears intentions as clear as crystal. At this point it's totally undeniable that any market associated with the Bears will be negatively effected by that association.
But for sake of argument lets say that you're right; being lumped with the Bears won't help Adelaide either, and something merely not hurting you isn't a very good argument to do it either.
The only reason people like you want the Bears involved in the discussion at all is because it'd make you feel good and appeal to your sense of nostalgia. Here's the thing though, the team wouldn't be for you or me, it'd be for the people of Adelaide. Given that maybe we should allow the people of Adelaide the freedom to build it as they see fit, and how they think it'll be most successful, not lump them with the baggage of Sydney's past.
Only because zero effort has been put into building the second tier up as a product in it's own right and promoting it.
I'm not saying that a second tier comp will ever be as big as the NRL is, but done right it could be a damn sight more successful than it is now, and big enough to sustain many of those smaller markets either aren't suitable for the NRL, or the NRL doesn't have space for yet.
I'd be willing to bet that a national NRL (or AFL FTM) second tier comp could be of a similar size to the A-league or NBL if it was set up right and promoted well.