L lenses are good. But they're not magic. They're still just lenses. They're expensive, big, heavy, and conspicous. I own the 24-105L, the 135L, and the 400/5.6L. I love them all with a passion and they're my most-used Canon lenses, but I also own the 85/1.8 USM and the EF-S 60mm f/2.8 USM Macro and I
know the EF-S 60 is the sharpest lens in my bag. And that the optical differences between my 85/1.8 USM and my 135L are smaller than you would think from the pricetags.
The 16-35 has gone through three versions (it began as a 17-35) and
some folks say they still haven't gotten it right. The fact that Nikon spectacularly HAS gotten it right with the 14-24 just makes it all that much tougher to accept that a $1700 lens isn't the be-all end-all full-frame ultrawide.