It has been suggested previously that reviewers should have their hearing regularly tested and the results should be published for the benefit of their readers but no one seems very willing to do it.
It has been suggested that many loudspeakers have their treble balance tilted upwards in order to catch the listener's attention during a short demo but another consequence of that could be that such speakers will actually sound better to those reviewers who are experiencing some loss of high frequency hearing.
Such speakers will be almost painful to listen to for those who have good high frequency hearing (16kHz+).
Saying flat is ideal always reminds me of philosophers who have very neat ideal theories which then bump up against real world experience;
Maybe, maybe not.
If what we're interested in is the accuracy of playback then we do want a flat frequency response at the point of delivery.
However, there is no good reason for the listener to then modify the signal to compensate for room acoustics, hearing issues, personal tastes etc.
As you say,
'This is why we have bass and treble controls too... to help compensate not only for our own individual hearing but also for our own personal preferences and purposes. It’s music, for crying out loud!' Taste matters.
It certainly does.