Variable Knockup

We have the technology. but really though, janna tornado knockup is reduced by tenacity(I think), or at least there is some sort of variation in the knockup, why can't tenacity reduce knockup cc, which happens to be over half of the cc in the game now?

EDIT: I suppose I probably should not use exaggeration in trying to prove my point, it lessens my impact. To clarify, I replace "knockup cc" with "displacement effects," if which none are reduced by tenacity. The point I'm trying to make here is that for most of the COMMON cc(Again, sorry for no clarification), there is no counterplay. you can't buy tenacity to reduce the displacement effect. in small knockbacks, it might be negligible, but in large knockbacks such as lee sins ult/xins ult or knockups in general(about the janna q, thanks for pointing the charging has to do with the knockup time), it would allow for shorter time to be disabled. while you are being knocked back or airborne, you cannot activate any abilities or contribute to the game. It is really a suppression with the bonus that no "exception abilities" (such as QSS or trynd's ult) cannot be activated either. I believe that tenacity should reduce the time for knockups and distance for knockbacks. Hopefully this makes more sense than the first time.