The 24 to 105mm is it an L series zoom with image stabilizer. I owned it for over 10 years, and made many beautiful pictures with it. It is extremely useful.
It's strength is its extensive focal length range. You have the focal lengths of 24 mm, 28 mm, 35 mm, 50mm, 70 mm, 85 mm, and 105 mm --in other words you have seven well-known focal lengths in one high-quality zoom lens that has ultrasonic motor focusing, and image stabilizer technology. The lens is designed to basically do almost every general purpose task.
My opinion is that the focal length range of 24 to 85 mm or 24 to 105 mm is vastly more useful for actual picture making than the 24 to 70 F/2.8. In today's digital era and speeds of 400 to 3200 ISO, the value of an F2.8 lens only becomes realized in the most marginal of lighting conditions.
I understand your fascination with
lens maximum aperture, but I think you are misguided in assuming that an f/ 2.8 lens is somehow inherently more useful and a better picture-maker than a lens with a much wider range of focal lengths but with a maximum aperture that is only one f/stop slower. I personally think that the 24 to 105 was one of the best zoom lenses I have ever owned from any maker in the general purpose category.
I grew up shooting a wide range of prime lenses from 24 to 200 and 300 mm in length, and I am not really a fan of the limitations that shorter and medium range prime lenses carry with them. However today, with many people coming from slow consumer lenses and going right to high-grade prime lenses, there is this fascination with what a single focal length lens can do. I'd likeb it to the tendency of many young people today to value style over substance in many things, such as cars, clothing, and musical artists. For example the singer Katy Perry… Very popular, but not a very capable musician… But pretty, and she makes good videos… But is she a real musical talent?
For example you mentioned the canon 85 mm F/1.2 lens....are you aware of that particular lens's extremely strong longitudinal chromatic aberration signature when used at wide lens apertures? Although many people rave about this lens, to me its bad longitudinal chromatic aberration signature, which is uncorrectable in post processing software,is a huge liability. and yet I have read many reviews, glowing reviews, of how beautiful the Bokeh is from this lens...when in reality I do not think it has beautiful bokeh,but rather offers a high degree of background blurring, which is not the same thing as Bokeh !