You're certainly right as to tilting, I never use this function, and, sacrilege?, never use tripods.I'm not into architecture, but in city "tourism"... Nevertheless, corner sharpness, compared to the TSE 24 II or even EF 14mm II,could benefit from some improvement. The corners are certainly sharp, but I'm convinced, looking at the latest TSE 50, 90 and 135, and Nikon 19mm TS, that corner sharpness could be improved.I don't agree. Using a tripod...the first thing you do with a shift movement is compose, meter (in Manual) and then focus. Then you shift the font element. The plane of focus stays the same. With tilt, you focus...then tilt, then re-focus and often then tilt a bit more and re-focus until your OCD gets a complete work out.
I've never had any issues with the corner sharpness of a TS-e 17L unshifted and it's not a lens that generally gets used wide open when shifted. It's designed for architecture and that generally needs stopping down for DOF.