One onsen is basically running a deficit because it's relying on an unknown agent donating expensive medicine to keep it operational, whereas the other onsen is directly powered by a minor deity who has got nothing else to do. This is like comparing a fossil fuel power plant to a hydro power plant. One needs to keep buying fuel whereas the other one needs to do absolutely nothing to generate power.
It seems to me the MC onsen merely needs to wait for a while and the competitor will suddenly go bankrupt.
The results might, no, will definitely be different if you test not only the satisfaction of the customers, but also the popularity and the quality of the onsen itself.