What you see is undoubtedly true if one compares line charts and zooms in to 1:1 in LR…but for many purposes the differences are overblown IMO. 2.8 is important if having that aperture is important for one‘s needs…but as in many things better is the enemy of good enough. Depending on where the output goes…I think that if I gave anybody a shot of something with the 2.8 and the 4.0 lens at the same aperture in on screen resolution they would be hard pressed to tell which was which on screen…which frankly is where most output goes these days. Some gets printed and some is indoors action where aperture leads to better ISO of course. I haven’t tested the wide lenses but for the teles I have…70-200, 100-400, 400/4.5 and 600PF when taking shots in good to medium light and looking at screen output resolutions it’s mighty hard to see much difference nd what o do see is more just different than this one is clearly better. I can say that the 24-120 almost immediately replaced the 24-70/4 as my walking around I only want to carry a single lens gear on whatever body I’m carrying for a particular outing…and if fast AF and FPS aren’t a big deal that day but light is then that body is likely to be the Z7II over my more expensive and heavy pair of bodies…because for that day the Z7II is good enough. I’m not ever going to say that Iq isn’t important…but a lot of reviewers and posters think of it as the Holy Grail when in reality good enough is good enough. Is better better? Sometimes it is, but sometimes it isn’t for a variety of reasons.
Not my experience. My editor (and I) pick up the difference between shots I take on the 24-70 2.8 and the 24-120 immediately. At identical iris and focal length, the transition from focus to out of focus is completely different, the background, especially highlights are completely different, the contrast is different, the color is different. Most of this is due to coatings and type of glass which are simply different. The aperture is the least important difference for me, shooting outdoors in daylight. I also think that because the 24-70 is such an important professional lens, they go over and beyond on flaring, distortions, etc.