This is all good and well, but you are doing OP a disservice by trying to convince him to not even consider the Meze. In the end of the day, what counts is what do you want from your headphones. Are these cans flat, transparent and reference-like? Absolutely not and I will be the first person to point out how much they deviate from neutrality.
The FR you brought represents them perfectly well, but your conclusion is misleading – one should look at the Herman response not as a goal to achieve, but as a standard to compare to. If you want a perfectly balanced sound that does not add or detract anything by itself, that is the target for that. but who really wants to listen to a flat, studio-like sound signature? Even in speakers most people apply some kind of a house curve to tweak the sound in a desirable way.
As I see it, in the sound domain the Meze 99 comes with a built in "house curve" that some people really find satisfying. The elevated levels in bass are perfect for delivering deep punches and full basslines in electronic and rock music. They also have very pleasing natural resonances in this area. The subdued lower treble takes away harshness from overly produced recordings. And the untouched upper treble keeps in the air and the presence, giving an overall V-shape sound signature, but not nearly as abrasive and fatiguing like most Beyerdynamic cans.
Plus, this would be a good time to mention they have really low distortion from 200 hz upwards (bass distortion is higher unfortunately), and a very good seal. Here are the Innerfidelity measurements:
https://www.innerfidelity.com/images/Meze99Classicwithnewpads.pdf
In other domains, the Meze are super comfortable, and a lot of people also admire their looks.
I personally tried listening to many dozens of closed back headphones trying to find something that sounds better to me than the Meze. So far I could not find it in any price getting close to these (the 2000$ Sony MDRZ1R are the only closed-back I liked more, and it's definitely has something to do with the Sonys being also not very neutral).
So the question said friend needs to ask him\herself is – what do I want my headphones to do? If the answer is to be super comfortable, kinda stylish, and deliver a bassy warm sound that doesn't cause fatigue, the Meze 99 should definitely be an option. If they want a super accurate and neutral sound signature that doesn't add any flavor of its own, than they should definitely stay away.