Looks like the Canon RF 28mm f/2.8 is a trip down memory lane, then. Shooting at f/2.8 produces somewhat soft images regardless of whether you are looking at the center of the image or the corners.
The Canon RF 24-105mm F2.8 L IS USM Z Lens vs. Canon RF 24-105mm F4 L IS USM Lens comparison shows the f/2.8 is far larger and heavier. The f/2.8 lens has 11 aperture blades vs. 9 (its blades also need to close farther to create the same aperture) and 82mm filter threads vs. 77.
It's sharp across the frame, it's decently fast, has IS, and is small/light! What's not to love? Well, the EF-S 18-55mm f/3.5-5.6 IS STM is f/3.5 at 23mm. That's only 2/3 of a stop and 1mm difference. Although the 18-55 isn't quite as sharp at that setting as the EF 24mm f/2.8 IS USM is wide open - it's decently close (there's a noticeable
ThsbmB.