They also realise the value in Brisbane, PNG and NZ too. All have their pros and cons. And yes, they're going to work with the franchises that offer them both the most value. PNG may be a long term government commitment to rugby league in the hundreds of millions. Christchurch has a new state of the art stadium. WA's main value is it's a large metro but it's behind on both the money and stadium fronts.
Furthermore, the NRL will also consider risk exposure. It may be that the government will cover the full cost of PNG. NZ has been more receptive to rugby league than WA. In WA's case, if you've got a Perth stand alone or a Perth Bears bid, the NRL will lean towards the Bears in terms of risk exposure. Also if the Cummins led group is too difficult to work, then they'll go with a different one. It might be a different WA consortium that's more willing to play ball. Or a different city altogether.
The point is I don't think any tenderer is in a position to set terms. Not WA, not the Bears and not anyone else. Again - the NRL 100% of the power here. If the WA government wants to get this over the line, they can't just beg - they need to go to the Pharoah Vlandys and offer some kind of financial tribute.