Just like how the TA compliments the IER and MDR as well. Having those cans makes it really hard to discern which device is better than the other. Still, the DMP is a collector piece, an eventual antique perhaps down the road
The DMP-Z1 is, of course, something different than the FiiO M17 for example.
Nobody will care about an M17 in most likely 5 years. Due to the shortage of AKM DACs FiiO kinda wants to make some of their products look like collector pieces (like the M11 Plus LTD or the K9 Pro), but AKM will recover, produce new DACs and then nobody will care about that old AKM DAC in the K9 Pro or M11 Plus LTD
It is actually pretty easy to create an device that produces an as perfect and flat/neutral sound as possible. But you don't buy an WM1Z, TA-ZH1ES or DMP-Z1 to mix/master/record music. You buy it to listen to music. If you hear an recording of an guitar, you don't want that it sounds like a recording, you want that it sounds like someone is sitting in front of you and is playing the actual guitar.
Sony does that with its unique technologies and most/mainly its self developed capacitors. The Sound of Sony devices is unique. The Sound of the FiiO M11 Plus LTD is the sound of THX AAA. Thats nothing bad, its just nothing special. Every company who builds an DAP and uses THX AAA Amps will most likely sound 99,9% identical.
That is why The M11 Plus LTD, M17 and so on are much cheaper. FiiO buys the hardware and tucks them together. It sounds and measures excellent, but natrual/flat/neutral.
The best sound is subjective, not objective. For me, i like Sonys Sound best. I play music myself and i know how instruments sound in real life. I want them to sound real when i listen to them and so far, only Sony devices gave me that.
There are technically better devices. The M17 is, on paper, better than the DMP-Z1 and i am sure it will measure much better. But if you listen to an recording of an guitar, with the DMP-Z1 it will sound like the guitar is really there. If you listen to it with the M17, it sounds like an perfect replication of an recording, but not an replication of the actual instrument. So for me, the DMP-Z1 (or WM1Z or TA-ZH1ES) is the winner.