Around sixty to seventy years passed between the time of the First Mt. Hua Sword Tournament and the end of ROCH. Let's call this the Era of the Greats, which encompasses up to at least a decade before the beginning of LOCH to the end of ROCH.
During the Era of the Greats, there was only minimal turnover at the top of wulin: other than swapping Gwok Jing, Yeung Gor, and Chow Bak Tung in for the deceased Hung 7 Gung, Au Yeung Fung, and Wong Chung Yeung (respectively), the roster of Greats from ten-plus years before the beginning of LOCH to the end of ROCH was more or less stable.
In the lower rungs of wulin, however, there was considerable turnover. Of the non-Greats fighters active in wulin at the beginning of LOCH, only Ohr Jen Ngok and 1 Deng's four disciples remained active. At least as far as characters we know, there was a near complete turnover of wulin (excluding the senior Greats) between the start of LOCH and the end of ROCH.
On average, how long do you estimate it takes for a near complete turnover of wulin...wherein say 90% of the prominent figures are replaced by newer, younger fighters?