I suspect you are right, but we're merely talking about choosing horses for courses. Compared with designing a normal zoom for an APS-C sensor, the complexities of designing a 16-35 lens to cover a FF sensor, where you are essentially wanting good image quality across a sensor with about three times the area, with a wider aperture make it a sgnificantly harder optical challenge. It shouldn't be a big shock that a lens designed specifically for an APS-C sensor performs as well or better than a lens designed with a FF sensor in mind. As metioned above, people don't get the full benefit of the "L".
Still, I wouldn't discount the use of "L" lenses entirely. In addition to sharpness, there is also light gathering, bokeh, weather sealing etc to consider. I used to love how my 70-200 performed on my 30D. (But then, I was never a fan of my 17-40 + 30D combo and picked up a 10-22 pretty quickly. Maybe there is a FF wide angle zoom problem?)
I have the same experience. My 17-40 on the 7D never impressed me. I also bought then the 10-22 which is doing a great job on the 7D. I even tought about selling the 17-40 at that time. After buying the 5Diii, my opinion changed however for the 17-40. That 17-40 is so much better on the 5Diii, also the 24-105 performance is better on the 5Diii.
It seems to me that the "L" versions do not allways get the max on APS-C sensors. However, my 70-200 is great on both devices. For a crop sensor I would never suggest to buy a 17-40, but do use the 10-22.
@ Mr Surapon: If the conditions are good then your 18-55 might do a great job or even a better job than the 16-35, however if conditions are worse (low light), the combo of 16-35 with a FF will be much beter.