If you are grinding mobs and doing absolutely every little bonus quest you will outlevel main story. Thats only natural so people that dont want to do that can still enjoy a natural flow while leveling. I have often noticed (started more chars) people on starting planet towards the end of class line there, beeing level 11 or so when myself i was level 9 with all sidequests completed. Only explanation i found was resting bonus or/and grinding random mobs. These people that probably include yourself brake their own gameplay flow by doing it wrong.