Interesting that you call it a "such a broad genre". I'd have said the opposite. I'd have said hardcore is what minor threat and bad brains did, and that it is / was a complete musical dead-end. When you start bringing in metal influences or it becomes being sceamo or emo it stops being hardcore. But I'd probably not be right.
I think that's where people are going to disagree with you. I think if you look at hardcore as a community led music scene, rather than a particular genre or sound, it's a lot broader than a handful of bands in the 80s. Perhaps musically a lot of what most people consider to be current hardcore wouldn't be so obviously linked to the bands you've mentioned, but if you look at the way the genre works, supported by a DIY community and driven by a desire to make music and live on your own terms, I'd argue that there's an obvious link to it's roots.
I think that's where people are going to disagree with you. I think if you look at hardcore as a community led music scene, rather than a particular genre or sound, it's a lot broader than a handful of bands in the 80s. Perhaps musically a lot of what most people consider to be current hardcore wouldn't be so obviously linked to the bands you've mentioned, but if you look at the way the genre works, supported by a DIY community and driven by a desire to make music and live on your own terms, I'd argue that there's an obvious link to it's roots.