Add higher level content

Hmm. While I have not started on Calculus I, II, and III, your annoyances seem valid, and I agree it would be nice to have a update for missions that have not been updated in awhile. While the feeling you get from seeing your low level classes percentages get lowered, I don’t have any ideas to help that. If you do, could you reply to my comment? A large amount of the people posting questions on zen desk right now are wondering the same thing.

Hoping the best for you, 

        Panzerkampfwagen

There is no problem with adding more "low level" practice questions for younger students, it helps them have a stronger foundation before moving on to the harder math! In fact, all the new added skills are outlined in this article and looks to me like more skills were added to higher level math (Alg I, AP Calc, Geo, etc) than low level math.
https://khanacademy.zendesk.com/hc/en-us/articles/115007408888-New-exercises-coming-to-missions-July-2017

I can understand the frustration, being a perfectionist I also like to see a lot of "100%" marks whenever I can, there is the mastery challenge that you can complete very quickly to knock out some of the easy skills.

As Khan academy is working on adding higher level content, I would urge you to remember that this website is completely free, and the existing content easily covers first year university in the subjects I've looked at so far, (Math, Electrical Engineering, Chemistry, Physics), it also covers second year university topics in Math and Electrical Engineering. I think we can all agree that that's a phenomenal body of lessons and knowledge even if it cost a thousand or so a year. The fact that it's free just makes it that much more amazing. 

Perhaps instead of complaining about how little progress there has been you would be interested in contributing to higher level courses directly, or contributing money to help fund new course creation. 

I'd love to see a Diff eq or linear algebra mission!!