For some reason, the "mid point of the season" is after Austria, which is only 9 races into the season.
**EDIT - this may be because if you win the first 9 races, it's impossible to be knocked off top by the actual mid point
Set the difficulty to medium or easy(depending on your own skill level) and you should win every race without any trouble(you will be between 2 seconds(monaco) to 8 seconds(Baku) faster than the opposition per lap).
After Austria, the achievement will pop. It it hasn't popped then, it should pop after Budapest