You are right. If you want to see Helsinki and the area around Bergen, a driving trip starting in Oslo wouldn't make any sense. On the other hand, if you don't want to drive in Finland, why not take the ferry to Stockholm and start the driving from there.
Also 9 days is not a lot. I would plan as a minimum Hki 1 night, Ferry to Stockholm 1 night, Stockholm 1 night, Oslo 1 night, on way to Bergen 1 night, Bergen 2 nights, on way to Stockholm 2 nights, Ferry 1 night, Helsinki 1 night.