Very interesting and thank you for making the comparison. I use the Umidigi S2 Pro (a rather unknown chinese phone) and I have similar results: 1500 steps (walking) for 1 km. As I am biking a lot, here comes the problem. 1 km biking is only 150-170 steps. Ok, biking (and the movements of the leg) is different to walking or jogging. But still, there is quite a difference.