My teammate doesn't seem to be improving

United States
Do the upgrades I apply to my car affect my teammate? I've been spending points as fast as I get them in order to stay competitive. While I am seeing great improvements with my results, Magnussen isn't following suite. If anything, he appears to be trending downward.

How can I get him to get better results?

I believe your teammate follows his own AI course. It might be that next season he leaves you for dust as he's spent this season doing boring groundwork things like reliability and longevity.