Regarding rules: Duh, of course it is. But beyond the use of the mechanical framework of OD&D, B/X, and AD&D, does the common reference frame of the D&D fantasy family still play any meaningful role within the OSR sphere? When was the last time you’ve seen someone talk about beholders, mind flayers, or displacer beast? It still happens, but when I see it, it tends to be regarding campaigns specifically set in Grayhawk or Forgotten Realms. What I don’t see is people describing their own creations which feel recognizably as D&D. Oldschool D&D seems to have very much become a style of playing, but has mostly disappeared as a style of fantasy.