My experiences with early Canon EF WA/UWA zooms were disappointing, as many people agree.
My EF 17-40mm F/4 L let me down many times in corner performance, and this was on an APS-H (1.3x crop) 1D Mk II, where the entire image circle is not used.
I heard the original EF 16-35mm f/2.8 L was a ‘dog,’ so when the Mk II version came out, I was hoping for improvements. I got a ‘bad’ copy with decentered elements showing up in the left corner (again, on APS-H.) I made some home brew test charts to verify and a PowerShot G9 beat it! I sent it in to Canon USA service centers three times to get this fixed, with no change. I even asked somebody at LensRentals for his opinion. I eventually sold this lens to someone at work who had a 5D with full disclosure and ‘try before you buy.’
My current EF 16-35mm f/4 L I’m happy with.
It seems Canon got serious about their WA/UWA primes and zooms and all’s good now in RF land.