IMO it doesn't matter what a mix sounds like on a "proper monitoring setup." If it sounds like shit on run of the mill small speakers, or in a car, then it's a shit mix.
Not saying this is a shit mix, but it's definitely not very exciting...
i don't recall anyone talking too deeply about what it sounded like on a "proper set up", as opposed to a consumer playback system...
...
but, there are very clearly issues with making ostensibly objective judgments about a particular elements with a mix, regardless of what level of system it is, and considering it a "fait accompli" that those judgments are unassailable.... so your point may be valid on the surface, but it's not as simple as all that when extracting judgments about the specific tonal character of a specific tone within in a mix....
EXAMPLE: i remember a few years back when Andy and I dropped in on Monte Conner at the Roardrunner offices in NYC.... he had recently given both andy and myself some grief about the low end in our mixes... he had a mid-line consumer stereo system in his office that he did all his listening on.... NOW, the point you make above would seem to apply, yes? because regardless of how poor the system was, he listened to everything on it and therefore his calls were still valid in that context, right?.....
wrong... Andy crawled under Monte's desk, right then and there. and found that he'd had the phase reversed on the little sub that came with the system... so Andy fixed that for him.
after that day Monte's remarks about low end changed considerably.
so yes.. it does matter, and the above is just one example, among various other possible reasons, why something about a room or system may distort perceptions and how the resulting judgments can seem to defy the good 'ol "i listen to everything on it" logic.
but, this was not a major point in this discussion.