NexGen was pushed by those with an understanding that it’s trimming the edges and not addressing”the problem”, which is, of course, real estate.
You need 2 minutes, or there about, to land and clear. There’s no amount of ATC tweaks that are going to fix that. Many, if not all “congested” airports don’t have a lack of ATC, but a lack of concrete because they’ve reached the this physical limit. Adding more RNP approaches or RNAV arrivals with profile descents isn’t going to change that one bit.
Even when they try to tweak the system to be more efficient, the people who lie underneath start squawking about it, and the richer the people, the less likely it will change no matter what, so again, the problem isn’t with ATC, real estate.
Marginal improvement? Sure, but it’s a lot of squeeze for the juice you get.