> I fear "Android" will continue to be understood as a word for either variant

Well, "Android" generally means either variant. I run GrapheneOS and I call it Android. If someone asks, I say I run Android, not GrapheneOS. Actually in terms of experience, it is Android to me.

But in a context where we oppose GrapheneOS to Android, then I think it's important to be clear. GrapheneOS belongs to the family of OSes that are based on AOSP (like Android, LineageOS, IodeOS, /e/OS, CalyxOS), while Android is itself a "subfamily" of that, including the Google Android, the Samsung Android, the Xiaomi Android, etc.

In a way, I personally feel like GrapheneOS is closer to Google Android than the Samsung Android is from the Google Android, if that makes sense. Moving from GrapheneOS to Google Android, I really don't see significant differences. Now Moving to a Samsung Android, I need to adapt a little.

All that to say, I really only make a difference when we are talking about AOSP-based systems as a distinct group, by opposition to "Android certified" systems. Just like it sometimes make sense to talk about GNU/Linux in specific conversations, but generally, we refer to a Linux distribution as "Linux".