Odd. Maybe it is a head to head fit thing because my Ananda have similar loudness all the way down to 20Hz as my Sundara and the HE6SE I sent you. I primarily use these because of the wonderful comfort and I find the sound to be pleasing both with and without EQ.I saw those too. As I noted in the review, no amount of pushing against the pads generated the sub-bass results they show. In addition, in listening tests the sub-bass is just not there. So I have good confidence in my measurements.
Hifiman headphones tend to exhibit a bump then sharp drop when their seal is broken strongly and only a mild roll off when the seal is only lightly compromised. Here is a video example (should be timestamped) of what an extreme example looks like.