Honestly, for hiking around Zion, the Canon RF 14-35mm f/4L IS USM is the more practical choice. Landscape photography usually happens at f/8 or f/11 to ensure a deep depth of field, so the f/2.8 aperture often goes unused during daylight hours. Carrying that extra weight of the Canon RF 15-35mm f/2.8L IS USM on long desert hauls can lead to fatigue, which is a real safety concern when you are navigating steep trails. That 14mm focal length is also surprisingly helpful for capturing the sheer scale of the canyon walls. While the f/2.8 is technically better for astro, the R5 sensor is clean enough to handle slightly higher ISOs if you want to try some star shots at f/4. Keeping your pack light and staying mobile is usually the better move for a successful trip. I always prefer reliability and weight management over features I wont actually use in the field.