@Ikarios Try to take the cups down a notch or two, it will sligthly weaken the clamping side force and will allow the cups to be less vertical and a little bit more diagonal thus weaken pressure against your upper ear (helix).
About the the mids you expected a 7506 kinda sound which is not what the 7520 is.
And I don't recall a post in this thread stating that the 7520 is a better 7506,
if I'm not wrong Mike F talked about it quite a bit saying that they are quite different sounding or maybe ti was the 7509...
Anyway after checking the 7506 freq response
it seems that I was right about my assumption that they have a bump in upperbass lower mids making voices sounding more authoritative/throaty.
No matter how long you will burn the 7520 you will not have those 7506 mids, But the good thing is that you could simply use EQ to achieve it quite easily then you might have a 7506 with better base.A 5db bump at 500hz and a 1db or 2db bump at 1000hz will be a good start for perfecting your equalization if you have control over Q's and specific freqs in your EQ will even be better.
Of course IMO comfort issue is a deal-breaker if it can't be overcome no matter how good a Headphone might sound it will always tinker with your mind and not allow you to truly appreciate its sound.