For me, I've learned to divide stax users into 3 buckets when it comes to the 009/007 conversation:
1. 007 lovers that just won't like headphones that are analytical ever.. i.e. same group that doesn't really enjoy the 009 and x9k
2. 009 lovers that don't enjoy the 007 as it's just not resolving enough.. i.e. same group that also really enjoys the x9k
3. Unicorns like myself that enjoy both lol (although I definitely fall more into bucket #2)
Apart from the slightly flabby bass and lesser dynamics, I don't hear other areas where the 007 is not resolving enough.
For sure the 009 pushes certain frequencies forward, like boosting clarity on an image, but I don't hear that as more resolving per se.
Alternatively, I can interpret the 007 as
more resolving, since it has this incredible 3D spatial focus on a solo or group of similar instruments or voices within the virtual stage, that I have not really witnessed anywhere else, other headphones either "decouple" them into separate parts, or not focus on them much.
I can only scientifically interpret this as the combination of a slightly over-emphasized upper treble (air) frequencies coupled to a fully isolating earpad design (at least on the stock Mk1) with a smaller cavity that makes L-R positioning quite precise, reducing crosstalk. Downside is that at other times, it can also feel that the two sides are 'too separated', while the slightly out-of-focus extra bit of crosstalk on an Omega makes its stage more uniform.
So besides 'evident detail', I also try to pay attention to how the sound of an instrument is rendered rather than the 'detail' it conveys, and if squeezing that few extra % comes with the compromise of a faster, drier, weightless sound (very fast, but smeared attack and decay, planar fans may especially notice that), it may not really worth it (for me).
I actually prefer the OG Lambda to both, if I had to choose one. For sure, there is a teeny bit of roll-off and bass texture is poor.
But: the "90% leftover sound" is a lot easier to interpret, a lot of harshness it being gently filtered out without being murky, no "spatiality tricks" (it's just simply spacious enough), macro-dynamic content that I call "bite" is very much relevant to the music (micro-dynamics are more of a big Stax territory) the physical damping in the housing with the "supposedly under-developed 1st-gen 2-micron thick diaphragm" makes images thicker, denser, rather than big holographs floating in space, and there is much more detail relevant to the music (the resolving power is still immense and far overwhelms the capability of the listener), leading to a more immersive, crystal-clear experience. To my ears, it seems one of the most "gimmick-free" estats out there (ymmv).
Sigma Pro is another real oddball, one of the most unbalanced FR from Stax, yet the "harmonic composition" and spatiality of the sound makes me adjust to its sound and still enjoy the music a lot more than what the measurements might indicate, it's not just about being too bright or too dark on a measuring rig, it is also about how that sound is "built up from the ground" - if that makes sense...