CDC provides credible COVID-19 health information to the U.S.
www.cdc.gov
So I may have not been as informed on my last comment, but the basic underlying thought that vaccinated people are a far lower risk to other vaccinated people still seems to be true - in theory if the park were to restrict to only vaccinated or tested guests there would still be some risk but far less than the current mixed scenario.
However, good point about testing - also, like I asked above, could the park provide a rapid test service at the gate?