Notwithstanding that the diffuse field curve is a choice that has fallen out of mainstream headphone design with good reason, I disagree that the group of curves are generally neutral and lack higher-Q features because the scale is hugely zoomed out.
FYI, the range on my plots is the standard 20 Hz to 20 kHz in frequency, and about 35-45 dB in total amplitude. The vertical axis is stretched out a bit from Ora's default setting to make some of the changes in amplitude across the frequency range a little easier to see and analyze. But that's about the only adjustment I made. Crinacle has a similar tool for adjusting the scale on the left margin of his graphs.
If you feel that the curves on the above plots are not neutral, then I'd be curious to hear which headphones you think might have a more neutral response in the treble and upper mids. The selection of headphones in Ora's graphing tool is somewhat limited, and doesn't include some of his most recent plots. So I just use what's there.
Here's the list of headphones from the 2nd grouping in my previous post, fwiw...
1More Triple Driver (perfect seal)
Beyerdynamic Custom One Pro Plus (velour pads, bass setting 3)
HFM HE400i (2020 pads)
HFM Sundara (2020 pads)
Monoprice M1570 (velour pads)
PSB M4U 8 (ANC on)
Verum 1 (leather pads)
I use these mainly as a guide for EQ-ing the treble and upper mids on my DT-770's. So some may lean a bit toward the brighter side of neutral. And they don't all have stellar response characteristics. But as a group, I think they're fairly ok.
I still prefer to use DF compensation, btw, because I think it still gives me a little better perspective on a headphone's tonal balance than the raw or Harman compensated plots do. It's just my opinion though.
I expect the overall shape of a neutral headphone's DF curve to roughly approximate a slope, somewhere on the order of -1 to -1.5 dBs per octave... not unlike the diffuse sound power response of a neutral loudspeaker. Some of the peaks and valleys in the treble and upper mids on Ora's plots make it a bit more complicated though.
There is also some smoothing on Ora's graphs, which could possibly be filtering out some narrower band peaks in the treble on some of the above headphones.
Higher Q is not in itself an issue, but when combined with significant magnitude of peak/dip, and the trouble it may imply for EQing is also not worth the trouble.