It's a good and frank review. The 17-40L is quite an old lens design, harking back to the early days of Digital SLR's. From a time where there were no dedicated standard lenses for the 1.6x crop and this was the closest thing. Full frame was only in the hands of the very lucky or super-rich.
The age of this lens doesn't undemine it's serious benefits and in fact offers buyers a really cost effective entry into the ultra wide range. For many, this is their first L lens. It's built like a tank and due to it's age, it's actually very keenly priced. Canon's f4 range offers a great compromise between cost, quality and weight / size. Just compare the 70-200 f2.8 to it's f4 variant to see what I mean. Canon is unique with their f4 offerings and for landscapers a 17-40L / 24-105L and 70-200/f4L offers top quality optics in a small but light bag, which costs about half of the f2.8 offerings...which is always a plus!
The L build quality is really excellent, way better than 3rd party lenses. There are other lenses on the market which can come close to this lens optically, but none are built as well, weather resistant and have such a quiet and reliable AF system. I went through two Tamron 17-35mm dii lenses before I realised that Canon's L lenses were far more rugged - end of story.
The slightly newer 16-35IIL offers a few more advantages over this f4 lens. Firstly it's a whole stop brighter, that's twice as bright and it's not much bigger or heavier. The other advantage is that it flares less and it's sun stars are a lot better. The lens has more aperture blades (and an odd number) helps create a more attractive star burst. While many would see this as a minimal advantage, for landscapers it's a delight and pushes their portfolio up a notch.
For my wedding work, I tend to not use a 24mm prime anymore, but favour my 16-35IIL. I have the versatility of the zoom and it's a tad wider than the 17-40L. I gain that all important extra stop and I like the look this lens creates in it's pictures. But it is a lot more expensive and it's extra features are not proportional to it's price, it doesn't have that much more to offer for it's extra money.