So since months ago hive added boosters, that allowed you to increase the xp you get in-game. Currently there is only boosters for TW and MM, and they are both 50% for 1 hour.
Actually boosters are costing 2$ or something (not sure), but I suggest to reduce the price by 50%. Otherwise boosters aren’t useful for grinding.
If you would like this to be implemented, please use the vote button at the top of the post.