So I'm not too familiar with how BotW is built, but from the looks of it they are not using an overall macro normal map, which would be sculpted per rock and section that gives the overall rock its shape. Instead they are using micro normal details (so a tiling bumpy rock surface) that tiles across the entire rock wall area. And because of the way the game functions and works, they are basically using designer geo (very simple shapes that the player interacts with 1:1), where a lot of modern titles would create a tile set of fully sculpted rocks with Macro and Micro normals/materials, that they then would be the wall out of modularly. But since the climb surface has to be pretty specific you cannot rely on that density of surfaces that may obstruct the player path and be very difficult to test.
There are ways around making a set locked off climable wall that then you could use a set of to make more detailed climable sections that have a higher fidelity, but they didn't seem it important to priotize it, which makes sense.
