Use of the article in “a better mechanic than [a] clerk”

These are a few examples in wren and martin English Grammar book related to the articles. Kindly explain the difference between these two sentences:

• He is a better mechanic than clerk.




• He is a better mechanic than a clerk (would make).

He would make a better statesman than a philosopher. (Would make) {what does would make in the bracket imply?