The only downside of the MT5s is that they are not very detailed. My active studio monitors the Adam Audio T5V shows more detail especially in the mids.
...that's a fair comment, though your T5V's do have extra 'air' in the upper mids from their tweeter design than most other monitors. They are v.good monitors for their budget but not perfect. Equally I've not come across a headphone that is perfect. Overall I find the MT5's to be more detailed that most headphones, but the highs are not hyped (where all Adams are slightly). For sure the MT5's can't match my Neumann KH120's for clarity (but they are 12x the price - and speakers in a room), though the MT5's do match the KH120's for overall sound signature - and I've found no other headphone that can come as close.
With the MT5's I'd say the mids are very strong, forward and detailed, the highs however do lack some extension - and it maybe this that you are hearing as a lack of detail in the mids. As a closed-back design there can be some resonance in the mids (they can shout/honk at high volumes) but this actually aids you in cleaning the mids in a mix. So I'd say they are missing about 15% to the top highs, but that's the only 'fault' I can find, as an overall package I score them higher than any other headphone I own or have used. Vocals are super detailed and present, if I put other headphones on, vocals can suddenly drop back in a mix, there's not really much wrong with the MT5's in terms of detail from what I hear, just the missing very top end highs.
The MT8's do have more detail in the high-mids - but this is due to the excessive presence of the highs - way too much, and lack of presence in the lows. The MT8's as an overall package score quite low to me - despite their slightly more open mids.
I'd say in the MT5 / MT8 price range if more 'detail' is required I'd use my DT770 80ohm (that do need to be driven by a music interface or amp). Though I couldn't use the DT700's for mastering as their EQ is out - especially bumped up in the mid-highs, nor actually for just listening as they can get painfully fatiguing - the honeymoon wow period when you first put them on doesn't last long. While the MT5's often 'disappear' on my head - a totally natural experience - and with that powerfully 'just right' low end.
BTW what headphone do you, or would you, use in preference to the MT5's?