What's the obsession with per-pixel FWC? Don't forget the pixels sit on a 36x24mm sensor, smaller pixels don't collect any less light, it's just there are more of them doing the same thing.
this 100MP 2.91um pixel has a FWC of 32800e-, if we do a 2x2 binning and use it as a 25MP sensor, the FWC increases to 131200e-, which is significantly higher than 24MP A7 III 95764e-.
Regarding diffraction, f/5.6 is a theoretical value yes, but in reality it's not clear cut like that https://fstoppers.com/education/5ds-f11-and-confusing-circles-68177