Indeed the default curve is quite problematic and with no EQ I'd prefer the HD650 over it. Personally I'm only interested in their potential EQability though, and while I'm not certain that anything past around 4kHz would fit the bill without additional tests performed, the HD650 also has issues above that frequency, essentially related to pad wear over time, and both will have some degree of variation above that frequency between individuals and between test rigs and individuals.
Since so much of the front volume for the MDR-MV1 is dictated by the memory foam pads, how they'll effectively compress when they're on my head, and how they'll wear out over time will be quite an important factor and could alter the ratio between the SPL below around 3-5kHz and above, if the MDR-MV1 behave under pad compression like most other largely vented fully open dynamic HPs.
Did you compare HD650 under the same test bench? Otherwise, any comment on FR is pointless...
Measurements processes and instrumentations are so different between reviewers that you may not fairly compare one FR to the other. BTW, the "HD650" dashed line on the graph quoted seems to be simulated FR with Oratory EQ. So hardly any comparaison to speak about here.
For these large over-ears with an open front volume there won't be a huge difference between decent 711 fixtures (soft pinnae) or even operators up to several kHz, and the measurements will translate fairly well to what actually happens on your own head - or at least a difference of a less significant magnitude than the trends observed when comparing the MV1 with the HD650.
The dashed line in the graphs above and below is the Harman target.
I've single out the ASR measurements as, as StaticV3 already mentioned, it shares a similar format with Aregina's. The HD650's sample variation can explain some of the differences above :
