Ok, I've done some comparisons between the MT220, MDR 7520 and HP100. Below are my impressions.
MY setup is Foobar 2000 FLAC -> ODAC -> Burson Soloist
Note that these impressions are not super-detailed, I mainly just jotted stuff down as I was listening to each one. So this is going to be a breakdown of that.
Bass -- HP100 = MT220 -> 7520
Mids -- HP100 = MT220 -> 7520
Treble -- HP100 -> MT220 -> 7520
Sounstage -- HP100 --> MT220 -> 7520
Imaging -- HP100 -> MT220 --> 7520
Comfort -- HP100 = MT220 -> 7520
Overall -- HP100 -> MT200 --> 7520
As you can see already, I preferred (barely) the HP100 to the MT220 and both of those to the 7520. What I can tell you is that the HP100 and MT220 are so close that it was almost hard to pick a winner. The main differences between the two are the slightly more treble air and bigger soundstage of the HP100.
Of course, one could argue that the MT220 is better since it has a smoother treble, meatier sound and more intimate soundstage. It's all down to preference really. I prefer the HP100's presentation (treble detail, soundstage and slightly tighter bass) but the MT220 is very good as well.
I'm torn honestly, I can easily recommend both headphones to someone looking for a closed can in this price range. I will also say that the MT220 is easier to drive than the HP100. The MT220 play fine from my iOS devices where the HP100 really needs a little amping to shine.
The 7520 was kind of like the odd man out here. To me, the real race was between the HP100 and MT220. The 7520 was a bit edgy in the mids and there was occasional harshness in the treble. It also sounded a bit metallic compared to the other two and to my ears had a sort of reverb-like soundstage thing going on. The 7520 had more bass than the other two, but to me, it seemed like more mid-bass where the HP100 and MT220 had deeper, tighter sub bass (which I love). I'm not saying the 7520 is worse than the other two, but to my ears, I definitely preferred the HP100 and MT220.
I actually compared the MT220 to my Philips X1 just for giggles and was surprised. Just a quick comparison, but to me, the MT220 sounds like a closed X1. Similar sound signatures, warmer, great bass while still maintaining excellent detail retrieval.
All in all, I'm very impressed with the MT220.
The 7520 does have the most resolution of them all though. Its just that the timbre is off. The tones are like you say. During bass tests I found the 7520 to have more resolution down low than even the th600 and some orthos. Its just not as tight as it needs to be and the midbass you mention next to the shouty mids and small soundstage makes it sound cramped. It does reach as low but the midbass makes it seem like it doesnt. I found the mt220 later on to be only average in bass detail and tightness but very dynamic and responsive to the track, amorphous even.