I mean that referring to "HN for X" is like (more than a decade ago) "Facebook for X".
I consider HN a clean exception to most (all?) online communities in which I have been participaing; in all other cases, the quality tanked, they became ghost towns, or they just changed from their original goal.
Sure, there are many wonderful forums and special interest groups, and it is good that new ones have been created. Just HN is not something you start at, it is something you become.