Here we compare Leica Summarit-M 35 f/2.5 (with the adapter) and Sony Sonnar T* FE 35mm f/2.8 ZA Lens (native E-mount) on Sony A7RM2. We use exactly the same settings in Manual Mode and on a tripod, with manual focus.
The overall optics is slightly different. Zeiss has a little more narrow view (maybe because Leica uses the adapter). Leica has a little more red.
The center looks sharp in both cases:
The corners are different – Leica has some smudging in the left bottom corner of the lamp shade – possible due to Sony sensor glass:
In general, both lenses are good. Zeiss has autofocus, and enables face, smile, and eye detect. It is a little bit bigger, but not much. manual focus is easy too. The aperture cannot be controlled via the lens.
I did not like the hood that came with Zeiss, so I put another one that I found on eBay.
When I want a Leica SL/SL2 (aka mirrorless Leica M) experience, I just use Sony body with a Leica lens. When I want a Sony mirrorless experience, I put Zeiss lens. The results are pretty much the same.