All tissues need stress to be healthy, and the bones are no exception. Without stress, bones will atrophy. This happens to astronauts who spend long journeys on the space station: their bones weaken due to no stress from gravity (they are weightless). So, we need to stress our bones, but tensile stresses don't work (pulling the bones apart do not stimulate growth). We need to compress the bones. In other words, they need to bear weight. (To learn more see this article
on antifragility and what happens if we don't stress our tissues.)
If a doctor has a patient with osteopenia (impoverished bones) or osteoporosis (porous bones) she may recommend walking. and walking will stress the bones in the legs, but they won't stress the spinal bones much. When we walk the stress on the spine is absorbed by the soft tissues: the muscles, ligaments and fascia. That is good, but it doesn't help the bones. So, how do we stress the bones in the spine? Yoga! Many yoga postures can do this but in Yin Yoga we deliberately target the vertebrae...think of poses like Sphinx pose: what do you feel? Hopefully you feel a stress along the back of the spine. This is the sensation of compression, which the bones need.
Compression on the bones stimulates the osteoblasts to become more active. Through a form of communication called mechanotransduction, the cells sense the stress in their matrix and become active. (I have written about this more here
.) So I would say compression increases osteoblast activity (not "quality" as you phrased it.)
Both yin and yang forms of exercise, and weight training as well, are good for our bones--they just have different targets. Which bones do you want to strengthen? Legs? Do standing yang postures! Spine, do yin postures. Arms? Do inversions like Handstand and Plank poses or weight training. Walking and running will also strengthen the legs. It is all good!