Hussar, how familiar are you actually with 2e Planescape? Because those numbers above you're pulling out of the plane of quasi-elemental vaccuum are really grossly incorrect. Seriously, compare the material on the planes that originated in 2e to the material presented in 3e, because the vast majority of it remained intact. 3e just didn't go into as elaborate detail, but heck, if you look at the 3e MotP there are some portions that are virtually word for word from 2e sources (some of the dreamscapes in the Ethereal plane), most of the locations originated in Planescape, etc. They didn't use Sigilian cant slang, but the lore was retained in very large part.
Even when 4e at first rejected the Great Wheel in favor of its own World Axis cosmology, you have to notice that over time a lot of Planescape material started to get ported in, adapted to fit in some cases, but ported in nonetheless. Plus, look at where we're at now in terms of planar design. Clearly the 2e/3e material had some serious traction or else the outcry over its excision in 4e wouldn't have been so extreme and we wouldn't be seeing it returned to core status in the game again like we appear to be in 5e.