Though I think a possible sick & twisted joke you could include here is that a human that figures this out hits depths of despair previously unknown so they actually do have a tangible difference in flavor
At least I think there's a certain existential horror someone would feel that not only have they seen a lot of pain & suffering and endured some themselves but that it's literally pointless
Maybe somebody figures out how to artificially synthesize the chemicals that the human brain produces when deeply distressed, using it to make unnaturally delicious blood.
And then has to avoid getting whacked by vampire lords who are pissed off about this "disrespect to the art form" and/or trying to cut in on their business.
'eh if you just tell a human they're on the hook for $10,000 and let them stew on it for a week you get 99% of the flavor you get from destroying everything they love over the course of a decade'
"let's blind taste test then'