I'm not sure if this is wrong but i'd have thought it was. I joined a league before the final race so that I didn't have to spend a season with a poor car. I had 170ish design points to use before Abu Dhabi which I used up. For the first race my entire car is 1?
Since you joined a league so late in their season, you essentially had no races completed in that season contributing to the development of your car's next season's design.