"Leaders (called elders) of a given congregation are selected from within..."
Looking at this from a JW perspective, it would have to be said that it's incorrect. Elders are not chosen "from within", they are chosen by Holy Spirit through the Governing Body. Of course that viewoint is subjective to what they believe.
However, I can see where someone who isn't a JW could say this and think it correct. Men from inside the congregation make up the elder body. Not counting missionary work, Bethel and traveling overseers, rarely is a brother appointed an elder to serve somewhere other than in his home congregation. The only change to elders is if someone moves in or is newly appointed from "within" so to speak.
"...and there is routine and frequent turnover."
I don't know about that one. I was born and raised in the religion and I still see serving in the city where I grew up the same elders that were around when I was a kid (except for those that have died or moved). New elders have moved in, brothers have been appointed, but except for the rare DFing or removal of an elder, once they're in, they're stayin'. I can still remember over a 20 some year span the couple of elders that stepped down just because they were tired. More have been DFd than have just quit from tiredness. The only meeting I've been to in the last three years has been the memorial, three years running, and the same elders have been there each time. One elder has been added that I know of, because he moved into the territory.