Well, I can tell you that I was pretty convinced that the cap is linked to salary too.
Now I think that the cap is still related to the salary but in a different way; if you train a lot one single skill you'll get the cap sooner and training one single skill a lot means also to have an higher salary that's why it is still related to the salary.
There is a lot of buzz that salary is not a cap, but combined skill point is, so if you could, test both theories to see which is more accurate.
Outside defense and inside shot contribute in a very minor way