I wonder if you meant to say the Leica S instead of the SL. The Leica SL is small format, and the Leica S medium format. The GFX will give a more medium format look over the SL with its larger sensor. I've been looking into getting a GFX instead of a X1D even though I like the appearance of the X1D.
Leica S lenses aren't priced like the Fuji G lenses, so I'm thinking the OP was talking about the SL. I'm not sure why a 24 MP FF camera is being cross-shopped with a 51 MP 33x44 mm one, though.
By the way, when I looked up current S lens pricing to make sure there hadn't been a sudden drop in S lens retail, I noticed that a new copy of the 120 macro was selling for $8200 at B&H, and they were selling a used one for $3800. I suspect that the disparity may have to do with the introduction of the GFX.
BTW, a new Fuji 120 macro for the GFX is $2700.
And, I just checked: even Leica SL lenses are a lot more expensive than G lenses, so now I'm confused as to what the OP meant.
Jim