Everything.What does that have to do with anything? I used that as an example because it's super distracing in both cases.
It's just as noticeable when you're speeding with roach and stuff just loads as you go. Unlike Rage 2, TW3 actually has a dedicated setting for this which pretty much fixes it.
Additionally it's not like Rage 2 does not have a dedicated setting for draw distance, it does it's called geometric setting. Pop ins are a result of draw distance, the faster you travel the more distance you have to travel and the more pop ins occur because things need to be drawn a lot faster for a lot further distance than you do when you are going slower. Witcher also has relatively denser environment so it can get away with having poor LOD for far off things as it'll get hidden/culled by things close off like heavy vegetation. In a less dense game your view is stretched out a lot further which further increases the likelihood of noticing pop ins and they'll be very noticeable even if they are very minor because the terrain is so openly visible.
Roach does not travel even half as fast, additionally take Spiderman for example the game's camera cannot travel faster than the max speed of Spiderman even in debug mode because it simply has not loaded things in. Point being draw distance and travel speeds are related.
Well that's not really a proper open world in traditional sense tbh, the actual play area is so small as you are limited to rooftops.