on the other hand, mining pool hub has HUGE issues with vardiff, (or had have not used it for over a month now) it negatively effects income, i had a detailed post about this some pages ago and there is no fix.
Share difficulty does not cause problems like this.
Low difficulty would cause higher bandwidth required to the pool and higher difficulty would cause lower bandwidth required to the pool.
As long as you keep mining and there are no connection issues then you get the same amount of shares.