I tested the X1D 30 mm and 45mm prime lenses against the comparable focal lengths of the GFX 32-64 Zoom at various apertures. Ordinarily, this would not be a fair fight, comparing a zoom against primes. However, the Fuji GFX zoom is a very impressive lens. Yes, the X1D prime lenses were somewhat "better" in terms of sharpness, but this was pixel peeping. Even in a big print, you may be hard pressed to see the differences. I decided that the optical quality of the lenses for the two systems was NOT a reason for me to choose one or the other system. There were other differences that I found much more significant.
One other difficulty with comparing lenses is that the GFX files with the Fuji lenses are quite sharp even when you thought you had turned off sharpening completely in LR. I have no idea if there is sharpening baked into the files or it's the microlenses on the Fuji sensor. Whatever it is, it makes it hard to do an apples to apples comparison. What I did was turn the Sharpening in LR down to 0% on both sets of files and use Focus Magic to taste for pre-sharpening.
I don't understand the physics behind the Fuji microlenses, but if they really do produce sharper files, you have to ask why no one has done the same sort of thing in the past. Did Fuji really figure out something that nobody else knew? Or, did Fuji accept certain trade offs in moire and aliasing that would appear in raw files but that Fuji could "correct" in its JPEGs? Fuji does seem to be shockingly obsessed about its JPEGs for the GFX given it is styled as a "professional" camera. Fuji still thinks it is in the film business, and considers JPEGs to be the "film."