As someone who frequently commutes in Teslas, I would say Tesla is closest to actually deploying something close to self-driving to the general population out of all the current self-driving competitors. Furthermore, I imagine they're collecting data on all the Tesla cars currently being driven.
I have seen the model updates substantially improve the auto-pilot capabilities with every update. And as someone who works with lots of quantitative data on a daily basis, I think there is a fundamental difference between training on billions of miles of simulated data vs. actual data. Simulated data may reduce overfitting, but there is still scope to overfit compared to raw data gathered from the field. Simply put, you won't generalize as well to data that's been simulated vs. field-generated data.