[jessriedel]

> Yuan Cao ... was clearly the one who actually made the pivotal discovery

Are you saying that based on something external to the paper? In the author contribution section, Cao is not credited with having done anything on his own:

> Author Contributions

> Y.C., J.Y.L., J.D.S-Y fabricated the devices and performed transport measurements. Y.C., V.F. performed data analysis. P.J.H. supervised the project. S.F. and E.K. provided numerical calculations. S.L.T., A.D. and R.C.A. measured capacitance data. K.W. and T.T. provided h-BN devices. Y.C., V.F., and P.J.H. wrote the paper with input from all authors.

The first authorship is an important meaningful thing, but it definitely isn't a guarantee that they key, most noteworthy step was done by the first author, much less the first author alone.