I usually take my 24-70/2.8 hiking on my R5 II. However I finally think it is too heavy. What would be a decent RF lens to get for hiking. The L are just too heavy for 5-10 mile hike. I understand IQ would not be as good but I am OK with that.
EF 24-70 f2.8 950g + adapter 110g = 1060g
Here are most of the zoom options covering similar focal length range:-
RF 24-250 f4-6.3 IS = 750g
RF 24-105 f4 L IS = 700g
RF 28-70 f2.8 IS = 495g
RF 24-105 f4-7.1 IS = 395g
Sigma 18-50 f2.8 = 290g (17mp APS-C crop)
RF 24-50 f4.5-6.3 IS = 270g
The weight saving ranges from fairly subtle to pretty huge. Likewise with the size. Generally, you make more compromises as you get smaller and lighter, not surprisingly. Also quite a big price range. Depends on what you are prepared to compromise on.
The RF 24-105 f4 L is a great all-rounder with very good IQ, versatile range, IS and fairly fast aperture, but may not offer you the weight saving you are after. Still quite a lot smaller than your 24-70+adapter though. The most expensive option.
The RF 28-70 f2.8 would offer a pretty big size and weight reduction with only a compromise on range at the wide end. IQ should be better than your 24-70. Still quite pricey.
If you really wanted to prioritise size and weight reduction, the RF 24-50 is a viable option for landscape type work IMO, as it has good sharpness across the frame throughout its range, and the slow aperture should not be much of a compromise for this kind of work, especially with combined IBIS and IS. Yes it stops at 50mm, but 17mp APS-C crop mode should still give you good results with an effective focal length of 80mm.
The Sigma is worth considering IMO as it's again very small and light, good IQ and maintains the fast aperture if that is important to you. Of course you will be limited to 17mp APS-C, no IS, but the IBIS will mitigate to a large extent.
The 24-105 f4-7.1 is another valid option with a different set of compromises - good range and IS but slow aperture. IQ is not great at the wide end but pretty good elsewhere.