So, most humanoids you see that are relatively cost-effective are just "humanoid" in that they look like humans, but there are significant mechanical differences between them and real humans. It's almost always driven by the cost of manufacturing different components. A good example is the lead screw you see in the knee and ankle on Optimus - while it is more human-centric to have tendon-like actuation, it drives the price up quite a bit. Put differently, humans have a lot of specialization which is not great if you want to mass manufacture something.
For walking, the most important thing is that the robot can be simulated well, so in our case, we tried to model the foot contact with the ground in simulation quite accurately. In fact, we found that force sensors in the foot probably help but they're not necessary in simulation, and we wanted to shave off anything that wasn't necessary. I am not sure how close we will get to human mobility - it's definitely a learning process - but you can get much further in simulation than you'd expect.
For walking, the most important thing is that the robot can be simulated well, so in our case, we tried to model the foot contact with the ground in simulation quite accurately. In fact, we found that force sensors in the foot probably help but they're not necessary in simulation, and we wanted to shave off anything that wasn't necessary. I am not sure how close we will get to human mobility - it's definitely a learning process - but you can get much further in simulation than you'd expect.