It seems Kipling is damned whatever he does. He writes a poem which expresses the idea (possibly startling for its time) that an Indian might be a better man than a British soldier, and is condemned for not writing it from Gunga Din's point of view. Such a poem would undoubtedly show a different viewpoint, but that misses the point. The poem carries such an impact, and still does today, because it comes from the viewpoint of someone who had regarded Gunga Din as his inferior and treated him as such, but then quite unprompted declared him to be the better man.

The poem is not about war, and the battle and the cause of it are entirely incidental.

Neither do I agree that Kipling was a spokesman for the establishment. He was certainly an imperialist, and he undoubtedly supported some government policies. However he was also highly critical of other policies, and many of his poems warn about England's lack of preparedness for the threat from Germany. When WW1 came he initially strongly supported it, although it was then widely seen as a righteous war. However he later changed his mind, although possibly not before the death of his son.

Kipling was a human being, and you cannot simply reduce him, or any human being, to a few sweeping statements. We are all more complicated than that.