Hi and welcome to the forum:
I have the original EF 24-105L f/4 and the new RF 24-105L f/4, and am reasonably happy with both of them - I am on my second copy of the latter, having destroyed the first one part way through a project, and I found the quality consistent and good for both, and that was shooting with the less forgiving 45MP sensor of the R5.
However, as I constantly maintain, much depends on what you need out of the lens. By which I mean what you are going to shoot, under what conditions, and for what purpose. I tried the 24-70 L f/4 range and was impressed by them very much but, for my purposes, the cost and difference compared to the greater focal range of the 24-105 any difference in quality was, at best, marginal and the range won.
Pixel peeping for its own sake is a dubious experience, especially if fixating on corners - how often do you look at someone else's photos and closely examine the corners? Looking at my own images, under normal viewing conditions and after applying the default lens corrections for RAW images in PS, I see no real issue. That said, I don't spend my life shooting back-lit branches.
For example, the quality of output required for many websites, especially social media (such as FB) is very low and images are seriously downsized, perhaps a bit more resolution is required for digital display and small-medium prints, and on the other end of the scale is very large, detailed "Fine Art" images that one is going to sell at a premium and thus requires greatest quality. Mind you, if you look at some of the most celebrated images of the last century they would be regarded as lacking of sharpness, even for the time at which they were taken - they are celebrated for their content or expression. As Ansel Adams said 'there is nothing worse than a sharp image of a fuzzy concept'. The average person will look at an image from a comfortable distance for the size of the image and will hopefully concentrate on content that you are presenting to them - as a generalization, it is likely to be other photographers who pixel peep.
Add on top of that, consider the sophisticated software that now comes into play for lens correction and post-production, and it puts a lot less pressure on the pure optics of a lens, or allows capabilities that hitherto could not be approached purely by glass. This marriage of computational and optical photography is demonstrated with the RF 24-240 USM and RF 14-35 L f/4 lenses. Without lens correction, at the wide end, they present seriously compromised images with massive vignetting and distortion, but that is deliberately built into the design - noting that one of these is an L lens. They are corrected via algorithms for JPG in camera, or with lens correction for RAW in post to take all that away and make the image look very good indeed. This methodology has been around in cell phones for some time, but it is finally making it into conventional dedicated cameras to give performance in areas that would not be possible without massive cost and weight of optics. If this seems alien, consider that for film shooters lens correction was a totally alien concept as the product was a print or transparency - that all changed with digital - either through scanning film or via digital output, so the principle of melding software with optics is not new, just taken to a new level.
For general reviews, - like my colleagues, I am not a fan of the Northrop duo - I usually refer to Justin Abbott, and Cameralabs with Gordon Liang. Their reviews are detailed, but I don't take them as gospel - for example both of their reviews of the lenses I mentioned above were before they really understood the significance of the lens correction software and were spooked by it. Still, for those lenses that don't use this technology, I find them fairly indicative.
cheers, TREVOR
"The Amount of Misery expands to fill the space available"
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
