So, the PDAF is rated at -4 to 21 EV and the DPAF is rated at -6 to 18 EV based on Bryan's write up on the 1DX III.

So, theoretically, the DPAF should have out performed the PDAF on the 1DXIII. My thought would be to try another lens as 3rd party lenses do occasionally have impacts. For example, Canon lens on the R5, I can AF at pretty much the entire sensor. My Sigma lenses, just a subset in the center..