Zion is gonna be absolutely incredible!! Honestly, you are gonna have such a blast hiking around there. Regarding the lens choice... dont get too hung up on those corner sharpness tests you see online. In the real world, the Canon RF 24-105mm f/4L IS USM is a total beast for landscapes and its way more practical for a hike than the heavier f2.8 glass. I use mine all the time and here is why I think it wins for your trip:

• The extra reach to 105mm is amazing for those shots where you want to compress the canyon walls. 70mm just feels a bit short sometimes when you're looking at those distant peaks.
• You are gonna be shooting at f8 or f11 mostly, right? Paying the massive premium for the Canon RF 24-70mm f/2.8L IS USM makes zero sense for landscapes. Save that extra cash for a nice dinner after the hike!
• It is much lighter. Your back will definitely thank you after a few miles in the sun... If you really want to be budget conscious, look for a refurbished copy from Canon or even check out the Canon RF 24-105mm f/4-7.1 IS STM. It might sound crazy putting a cheap lens on an R5, but that little guy is super light and surprisingly sharp when stopped down! But honestly, the f4 L version is the absolute sweet spot for quality vs price imo.