I honestly can't say whether I was having problems with the original pair or not, or if it's just my ears. What I had noticed I was suddenly not noticing when comparing before shipping the first pair back, though either way the sound was still underwhelming compared to what I remember from those years ago.
So, my girlfriend is using them now, though she claimed to have noticed the muddled issue as well, and then not when comparing between the two. Maybe in those years not having PortaPros anymore I hyped them up before finally replacing them, maybe there's genuinely a difference between the Massdrop X variety and the originals, or maybe my ears are either worse or just more picky as I've had better headphones since. I just don't know.
What I do know is Massdrop is awesome and I'm grateful for their prompt, courteous, and understanding support, especially when I completely spaced they had already sent the return label, causing a larger than necessary delay in my returning the first pair back to them.