You know where game designers borrowed the yellow paint idea from? From real life. We do use color-coded markings all over the place so that people can quickly see hazards. We use literal yellow paint to demark trip hazards and ledges. We use green paint to mark emergency exits. We use red paint to mark medkits (first aid kits). We use green or blue paint to mark defibrilators. We use red, green, white and/or blue paint to mark dangerous road crossings or cycle paths, and so on. (Colors likely vary by region.)

Because real life is too detailed and “level design” is not enough to clearly show all the information necessary to avoid accidents and to find what you need in emergencies.

In the end, whether you use yellow paint, red paint, sparkles, outlines or lights to highlight interactible objects doesn’t matter at all. All of that is absolutely identical. If everyone would switch over to red sparkles, everyone would have the same complaint just about now red sparkles.

You don’t have to have low-poly art for this to work. Not everything in assassin’s creed was climbable. But you know when it was and when it wasn’t, do you didn’t even try to climb what wasn’t. You could climb vertical walls of mountain rock. You couldn’t climb up flat walls either, you had to have bricks sticking out. Granted, most buildings had something to grab onto. But you saw which elements you grabbed onto, if those weren’t there you would know why you can’t climb.

You might have quite a generous memory of assassin’s creed 1. I just loaded up some let’s play to look at it, and on the one hand the environment is super low poly, and on the other hand the wall textures really don’t give any hints of anything. What is there is that if the wall is perfectly, absolutely smooth, there’s nothing to hold on to climb up. If there’s any geometry at all on the wall it’s climbable.

That brings me back to my original point: In old, low-poly games, any object that exists is interactible. No need to mark these objects, because the marking is “object exists”. Try the same in modern near-photorealistic games. Doesn’t work like that, because here no wall is perfectly flat.