From that perspective, you have a valid point. I am not saying that you can get other lenses exactly the same range as the 24-105mm. I'm only saying that the lens is not very sharp. If that zoom range is very important to you, then you pretty much have no other choice because there are no other choices in that exact range. But like many people, IQ is very important for me. Also, I don't really care too much about zoom below 70mm because the reach is still small and can be easily taken care of by cutting down the distance (portrait vs body shot, for example), whereas a zoom like 70-200 or beyond is quite useful when trying to shoot from a distance. So having one prime lens in the range of 30-50mm and a zoom lens beyond 70mm, both of which have much better IQ and much further reach, is a much better alternative, at least for those who don't have your zoom needs.
OK, I agree entirely. If you want IQ get a 70-200 and/or a prime or two for sure (24-70II is supposed to be good, but I'd go the prime route myself). As I probably mentioned either before in this thread or others, I do agree this lens, while sharp in the very center, quickly gets quite soft. Compared with some of my other lenses I'm actually surprised at how sharp it is in the center at f8, but I am still bewildered by people that call this lens 'tack sharp' and wonder what they are comparing it to, or how they are comparing it.
And yes it has vignetting (all the way to f11 at 24mm), CA at each end (but definitely fixable, unlike my 18-55IS which seemed inconsistent) and bokeh that leaves something to be desired (or perhaps 'interestingly different').
I don't have my 18-55IS kit lens anymore, but when I bought the 24-105 I didn't get it to get better sharpness than the kit and didn't notice a night-and-day difference. I think what happens is that a lot of people go from a cheap lens to this and it does in fact meet their needs and they have spent $$$ on it so they rave about IQ. Or maybe they are just so good they can get great shots with a mediocre lens and 'blame' the lens for their good results?