What? the 24-105 is an L lens and a solid walk around choice. I bought the 24-105 well before upgrading my body. Are you thinking of the 24-105mm f/3.5-5.6?
They are not wrong in that it is bundled with the MkIII. But I feel like the demographic that purchases the MkIII aren't getting the 24-105 with it 'just cause'
It was a common kit lens for the 5D Mk III, and AFAIK in the pairing the lens limits the camera (edit: from a pure optical quality perspective). It's not a bad lens at all, but clearly an allrounder with compromises and not a specialist. (And thus a good kit lens and it's not a surprise many people use it, since getting a zoo of better lenses is really expensive and a lot to carry around)
IMO it's just the opposite. It's L-quality glass, and the IS makes it a decent performer for low-light and video as well. With the exception of pixel peeping, I'd feel far more limited with a single fast prime in most situations.
I meant "weaker" purely from an optical perspective: the camera has a higher resolution than the lens can deliver, at which point there's the question if the money isn't better spent elsewhere, assuming you don't have other reasons to go for the expensive high-end body. Generally a characteristic of bundled lenses: they are flexible and (with the better cameras) high in quality, but generally they don't reach the body in quality. (Although looking at tests again, it seems better than I remember the one I borrowed a while back)
And e.g. if i were to switch to full-frame, I don't need the extra length of the 24-105 and would go for a sharper off-brand 24-70 2.8 (although there is a new revision of the 24-105 around the corner), since I'd want to cover longer ranges with additional lenses anyways. But that option wasn't available when the Mk3 came out, and I totally get why people choose the 24-105.
> This is a $1,000 lens--definitely not a kit lens.
It is also definitely not an f/2.8 lens like all the other top lenses associated with this camera. I too have found it puzzling just like the parent did.
Lens speed is not the end-all be-all of photography. The 24-105L is significantly longer and has image stabilization. Sometimes the ability to handhold with a shutter speed 2-3 stops slower trumps the ability to increase the shutter speed 1 stop.
IS lenses are generally considered better for all-around photography, particularly for subjects which do not move like landscapes. Faster lenses give you more ability to stop the action of a moving subject and a shallower depth of field (given equivalent focal length).
The 24-105L is probably the most solid general-purpose lens for a full-frame in Canon's lineup, it's silly to disregard it just because they offer a bundle with full-frame bodies.
All you say is correct and I agree that lens speed is not the only element to consider. As you noted, it is a trade-off between different factors.
My main gripe with the 24-105L vs. the 24-70L (i.e. the lens that came second in that chart) is not just speed in itself, but the fact that the former has a zoom extension of more than 4X (my previous comment should have been more exhaustive).
As an old-style guy, I usually am uneasy with zoom ratios over 3X because I believe they are detrimental to quality. So when I have to trade between zoom extension vs. something else, I often go for the latter. The MTF charts for the 24-105 f/4 L [1] and the 24-70 f/2.8 L II [2] seem to confirm my gut feeling...
If you can only afford one lens, it's a fine all-around piece. It just isn't as good as some other choices. Many have complained that it is too soft. I was explaining why this combo is at the top of the list and commenting that it's popular, but not "the best" combo.
[EDIT: Apparently it was available as a bundle at one point.]