Thanks for everyone's responses!
Apologies for my negativity in the OP but the best way to get people to tell you why they like something is to tell them you dislike it ¯\_(ツ)_/¯
What I'm hearing is it's not for me. I was in a position where I was under the impression that Graphene would offer me more control of my device than stock android, whereas it seems it leans more towards "ownership" than "control". (i realise that's poorly worded. what i mean is "custody" and "control" can be synonyms, but "having control of" and "being able to control" are not the same thing). Ownership is very cool, and I realise that simply flashing magisk or similar won't afford me that, but when I can use root capabilities to turn off specific undesirables, that's good enough for me.
Furthermore, I promise I'm not trying to be rude or combatitve here but the lack of any user's response (across both forums!) to this part of the OP:
When I encountered technical problems with android, I had a 3-billion-strong userbase's worth of people who had found solutions before me. Is that worth losing for graphene?
Is uh... telling.
But just because I've not been convinced by y'all doesn't mean that I'm not thankful for this thread - it has been useful to me in making and informed choice, and may well be useful to future people who are in my position, who may end up deciding in favor of Graphene due to being more informed by this thread. I'm not going to reply to everyone (though I will to a couple of the weird ones), but you've all been helpful.
Thanks again!