Upload & Sell: On
I still say the 17mm T&S coves it.
The TS-E 17/4L is a benchmark in lens performance, between 14mm and 24mm. OTOH, the Zeiss 18/3.5 ZE is a lot smaller, uses 'normal' filters (as opposed to the TS-E 17 "bug eye"), and the 18 ZE is another of the few other benchmark lenses in this range.
N.B. the 21 ZE is another most-excellent lens in this range, but it's too close in focal length to 24mm for me. I found I'd almost always use my TS-E 24/3.5L II or 24-xxL zoom, instead of the 21 ZE, so I sold the 21 ZE. Now, I use the TS-E 17/4L when I need movements, and I use the 18 ZE when I don't.