The report they are citing (https://www.ussc.edu.au/analysis/averting-crisis-american-strategy-military-spending-and-collective-defence-in-the-indo-pacific http

The report they are citing (https://www.ussc.edu.au/analysis/averting-crisis-american-strategy-military-spending-and-collective-defence-in-the-indo-pacific https://www.ussc.edu.au/analysis/averting-crisis-american-st... if you didn't see the link) is much more interesting. Though it doesn't seem to cite a source or give evidence for the claim that the missiles could overwhelm US forces within hours, and there doesn't seem to be any elaboration about that figure. Honestly I don't think they are taking into account ballistic missile defense systems in place, the rate of fire the PLA can sustain, the risk of escalation (depending on the scenario, some of the countries these bases reside in could be neutral in the conflict), and the fact that the PLA will likely want to hold on to their longer-range DF-26 missiles until they get the opportunity to take down a carrier.