The majority of single track trails in the Sierra Nevada are neither free of anything which you can trip over, nor proper T2 where you are moving over a constant uneven surface. Just because there’s some obstacles in the trail doesn’t mean that it’s hard to see where it goes or that you need boots - many times you can walk around obstacles on a trail. It’s also pretty common for people to hike off trail in rugged terrain with low top approach shoes. My partner will carry a heavy pack on T2-T4 terrain with minimalist trail runners.
I also read well cleared as that vegetation will be cut back and branches removed from the trail, not that every single rock and root has been taken out of the path. In order to be visible it just needs to be easily distinguishable from the ground around it - a trail can have a lot of roots on a dirt surface and still be clearly distinct from thick vegetation on either side.
None of the photos on Key:trail_visibility - OpenStreetMap Wiki show trails completely free of obstacles.
This sounds like my proposed hiking_technique. I’ve been thinking about the obstacle issue I outlined above over the summer, and someone else in the thread made a point about it as well.