I can think of one route that is operated by both eJet's and F100's under two different mining contracts (Groote)
It's not a route, it's a destination. Airnorth fly to/from Darwin, Alliance flies to/from Cairns. Airnorth has work for the aircraft once back in DRW, Alliance has work for the aircraft once back in CNS. Different economics.
eJet's also operated The Granites run on behalf of Alliance until they re-opened their Darwin base.
I don't know if that indicates the operating costs are similar. What it means to me is that Alliance needed someone/anyone to operate their route until they could put their own aircraft on it. It seems it was cheaper to set up a base with all it's associated costs and use Fokkers for one FIFO contract, than pay someone else who was already there to do it for you using something else.