How would the davis-moore thesis explain the fact that physicians earn far more money than bus drivers?

The occupation of physician is more highly valued than that of bus driver and requires much more sacrifice in terms of education and training. This lead to only a handful of people could become a physician but many more could took the job as bus driver.
Since the physician is significantly 'rarer' and harder to train compared to bus driver, society reward the job with higher pay.

The answer is society was a caste like system with poor whites at the bottom of the white social ladder.