the world doesn't work that way. Just because mcdonalds opens 3 new stores in the same suburb doesn't mean it's going to wipe out KFC in that suburb....
You are 100% right in what you are saying but the analogy isn't apt here. Rugby League has been the dominant sport in Moreton Bay, North Brisbane and the Sunshine Coast for many decades. The Lions / AFL started to invest in the grass roots in Burpengary, Moreton Bay and Sunshine Coast a decade or so ago. They've got an academy up there somewhere. They were really trying to eat away at our dominance.
The Dolphins being promoted to the NRL and being tasked with that whole region would be very concerning to them. Not only the presence of a team synonymous with the region but one that has been mandated to spend on grass roots as a condition of their entry.
Ask anyone at AFLHQ or the Lions and if they are being honest it is a massive blow for them. A Western Corridor team would dampen their plans out that way too.
Yes, of course the Lions always will exist, there are too many Prictorians here for them not to, but NRL is doing good things here to make sure RL is the number 1 game forever in SEQ.