You must be doing longer flights as mentioned earlier for shorter flights (I typically do flights less than 2 hrs) setting gate as starting point MSFS world map after SimBrief import significantly alters the flight plan.
As much as I would like to use 3rd party ATC - I don’t know if there is any 3rd party ATC that works well with MSFS live traffic + AIG? The immersion of that is quite nice.