Assuming both MTF charts were comparably computed (neither is measured AFAIK), it’s looks to me that at 24mm, the Nikon NIKKOR Z 24-70mm f/4S will deliver significantly higher image quality past the 10mm-from-center offset (about the central half of the frame). Beyond that central 1/2 of the frame, the Canon RF 24-105mm f/4L IS drops off steadily and with notably greater astigmatism. Moreover what is most important for immediate visual impact is high contrast at 10 lp/mm, and there the Nikon starts and remains higher as good as the very best wide angle available today at the same f/4 aperture.
The main thing is this: the Canon RF 24-105mm f/4L drops off sharply in performance from just before frame edge (around 17mm offset) into the corners. Thus it would not be my first choice for a landscape lens. Still, it might improve quite a bit by f/8 and thus is going to make a lot of Canon shooters very happy—smaller and lighter and mor or less the same performance as the Canon EF 24-105mm f/4L IS II. The Canon RF 28-70mm f/2L offers considerably better performance at nearly triple the price.
Conclusion (24mm): a mid-range zoom might or might not be a justification for choosing a new mirrorless system, but if it is to be the lens shot most of time near the wide end, then on an optical basis Nikon easily looks to be the winner.
It’s hard to compare the Canon RF 24-105mm f/4 IS to the Nikon NIKKOR Z 24-70mm f/4 S at the telephoto end because of the differing zoom range—not MTF chart for 70mm on the Canon lens. My bet would be that the Nikon offering outperforms the Canon offering in the 24-70mm range.
Which is “better”?
“Better” is a value judgment. While the Nikon looks better optically, the Canon RF 24-70/L offers the additional 70-105mm range. Since the Nikon Z7 offers in-body image stabilization, I call it a draw on that feature, though possibly the Canon lens stabilization is better, particularly at the wide end).