What is the best landscape lens for the Canon EOS R5?

So Ive been shooting on the R5 for about two years now mostly for weddings and some wildlife but Im heading out to the Dolomites in literally ten days and I realized my old EF 16-35mm f/2.8 II is just... not it. I tried some test shots yesterday and on this 45MP sensor the corner softness is driving me absolutely insane especially since Im planning on doing some huge prints later this year. Ive always been a glass-first kind of guy but Im stuck between the RF 15-35mm f/2.8 and that 14-35mm f/4.

The f/2.8 is tempting for astro if I get a clear night but honestly Im worried about the weight since were hiking like 10 miles a day. Then again Ive heard the 14-35 has some pretty crazy distortion that the camera has to fix in-post and Im worried thats gonna eat into my resolution or make the edges look weirdly stretched. Budget is flexible but Id like to stay under $2400 if possible. Does anyone have real-world experience with these two on the R5 specifically for high-detail landscape work? Is the extra 1mm on the wide end worth the f/4 trade-off or should I just suck it up and carry the heavy 2.8? My flight is next Friday so I gotta pull the trigger on an order tonight...