There are a lot of variables here but it probably is just an error of how fourier transform is used in the application. Still there could be more problems with the dac and/ or method of EQ. There are many ways of making digital EQ filters.

The graphs are pointless since the models are different and high frequencies are always going to be different(ear to ear) even if the graphs match.

I don't like the harman preset on a sundara(especially for the bass, probably the same case for edition Xs)

Exactly the codecs like LDAC, AAC, SBC tipically are mentioned when just audio is sent to a headphone/earbud, not when the mic audio is in use. It is another mess when it is about codecs that take in count the mic.

Those headphones may have a frequency response over 20kHz, but that is a diffuse information, you could have 30kHz with 60dB less than 1kHz and still be considered to have a frequency response over 20kHz, the company will set its own way to represent the limit.

Like if you go that cheap a dac is actually a bonus

No, I use EQ too

On windows it is possible to use Windows Subsytem for Android and install apple music(android version) from apkhere(or another store?). It is a weird process but possible and still better than tidal + not everyone needs exclusive mode, if the quality is above 16bit 44.1kHz like what apple music gives why taking so much importance if a resampling is not going to change anyhting to a 96kHz record(at least not anything audible)

Apple music is actually good

It was talking about parametric EQ although a graphic eq could also help knowing your taste. For parametric eq it is better to use android or windows. On mac the choices are not easy and ios is just not viable for parametric eq as far as I know.

Bandcamp

Have you compared the wired xm4 to the skullcandy or just wireless?