It sounds to me like your DM is maybe just used to a very low-optimization group. You're not overpowered in the great scale of the game, but it can be a nasty shock to a DM to run into a character that does something reasonably effectively if the rest of the group normally struggles with challenges as written in a module (note: pre-written modules are notorious for generally being quite soft. A 9th-level module is likely to be a pretty appropriate task or even easy for an optimized 6th-level party.)