As far as I know the amount of pain is not an indicator of how mild or advanced your endo is. Birth control is a hormone and hormones are generally a great way to treat endo, and many people say that their symptoms are not as bad on birth control. Same with hormonal IUDs and the shot :)

Absolutely I had very mild pain while on birth control. The excruciating pain honestly didn't start until right before I got my tubes tied. They found my Endo then and when burnt off and was pain free for 6 months.