Who's that Harm
on guy?
I might seem like an audio monster, but to me variations in bass treble preferences of 1 or 1.5dB are not really significant for entire groups of listeners. I mean it is because it's audible, but at the same time you will often observe that much change from how people place some headphones on their head, if they wear glasses, etc. And you will find bigger variations between listeners' HRTF.
On the other hand, and despite my expectation that individual HRTF would have a huge impact on preferences, the results over countries, age, sex, training, music genre were still a consistent move to raise the bass and lower the treble of the initial response. That was a real surprise for me and is IMO a strong indication that we all at least aim for a pretty similar frequency target ballpark. Nothing suggesting we want the crazy variations we can find between 2 typical headphones.
I'd still personally take simulation of some speakers measured at my ears over all this. I'm a Realizer A16 owner and fanboy, and I was using bad DIY convolution for years before that to simulate speakers at 30°, and EQ+crossfeed before that. Sadly it's still not something you can hope to find everywhere with a cheap and accurate method. I'd say it's coming, but I've been saying that for the last 20 years. At this point I'm like my grandpa who used to say "death is coming! You laugh but one day you'll see I was right!".
So in the meantime, if I had to advise a friend, I'd tell him to start with that Harman curve and just fool around with simple bass or trebles EQ. That's assuming he's not able to do anything more complicated with an EQ because of lack of experience. But if he was able to, he wouldn't need any help from a target curve in the first place. That's why I think it's fair to make the "noob with EQ" assumption for the general population, and conclude that they would benefit from the Harman reference.