I have the 24-70 and use it regularly for portraits, weddings, etc.
I haven't taken the time to compare at pixel level, but its adequate for the jobs and print sizes that are likely to be used.
If in needed a critically sharp lens for a job, I'd likely use a macro or prime. If I need flexibility for fast moving situation then zooms and the 24-70 suits.
Entire wedding last Saturday was shot with it. No problems with softness, except when it was slow shutter speed and movement. Not the fault of the lens.
My opinion of most web reviewers is that they look at pixels searching for something to say that will get them clicks on their site to generate revenue. Are all the reviews or reviewers worthless, no. But, in the end I want to have the lens in my hands, evaluate it and make my own decision, based on the specific lens I have and my needs.
Here are some examples of what I mean from Art Expo Chicago last Thursday.
All were shot with Auto ISO, Av, minimum shutter speed 1/100, F4.
The motorcycle image is ISO 2500, as is the off hand portrait of an artist.
The modernist head is ISO 2000 and the endless reflection is ISO 800. All are 1/100 at F4.
Even at 1:1 all are good images for noise, sharpness and that's without any work in Lightroom or photoshop.
The endless reflection was corrected for white balance, the others are essentially straight out of the camera with maybe some cropping.