Look no further than our Captain, Paul Pierce.
PP started out at 71% and improved to approx. 86%. From '06-11, he improved every year but 1.
And Rondo has regressed every single year, moving from 65% to 57% over the course of 5 seasons. He has regressed every year but one.
So, I guess we should expect him to threaten the immortal achievements of DeAndre Jordan and Andris Biedrins in a couple of seasons.
P.S. Also, "yips" refers to a "sudden loss of fine motor skills". Rondo hasn't "suddenly lost" anything -- he has never been a great, even good, free throw shooter to begin with.