I've had the GH3, GH4, GH5 and now S1H. Love them all. It's the exact same frame of view I really don't understand what others here are talking about. View is not cropped??!!
S1H with the 24-70 lens does seem a bit sharper with wider apertures than the equivalent on the GH5, and low light performance is improved but nothing earth shattering at all.
I still have the GH5 and will still be using it as needed.
I must admit loving the flexibility to zoom 24-70 and maintain sharp/ fast vs swapping primes on GH5. That's the single biggest advantage to me.
Still need 100-400 + GH5 so I don't have to carry around a FF bazooka lol