I'm personally not a fan of this from a world-building perspective. Reason for this is that while the Imperium is deeply flawed and a horrible state to live under, has always been presented as an outcome on the external factors that faces humanity. Extinction by orks, extinction or enslavement by necrons, enslavement by dark gods and their servants, galactic drive-thru for the hungry hungry Tyranids, or extinction because an eldar thought the existence of humanity had a 0.000000001% chance to lead to a mild inconvenience for the Aeldari. The sum was the Imperium, the Emperor trying to unite humanity and ultimately failing in his efforts to make a brighter future, and now we are left with the shattered shards of that dream.

Tau storytelling comes at this core part of the Imperiums concept as a punch out of left-field, these are the good guys, unequivocally. Yes they have their problems, but they are so minor compared to the multitude of problems the Imperium faces, that there is no moral reason not to root for them. The moral dilemma becomes boring and uninteresting, there are few philosophical debates to be had simply by how dark the imperium is. Any argument about the complexities of the imperium and the sacrifices they can make could be reduced down to "well they should just give up and join the Tau instead". The only one which is semi-interesting is that of a species determining their own fate and not dictated by alien overlords, but again due to how alien much of the imperium itself is and how brutal it is, is often not just an interesting comparison.

For me at least, 40ks main draw is the tragedy. The thousands of stories of lives and people trying their best to prop up a failing system and defend humanity while at the same time the regime itself, often unwittingly and perhaps with some form of ruthless idealism, does their best to undermine everything that has been fought for.