iPhones will report this, at least with Airpods and presumably Beats. It’s in Control Center -> Hearing. They know the sensitivity of their own devices, so they can calculate the loudness. I have also seen this in screenshots of at least one the third party phone apps that many headphones come with.
I have little-to-no FOMO. I’m happy with my EQ’d 6XX. I know there are objectively better headphones, and I’m sure that there are headphones that would be subjectively better for me. But they sound fantastic. If I wanted to spend a grand auditioning similar headphones or springing for the next tier, I’d rather get a new fork for my mountain bike instead.