Hmm, I'm not sure about this poem (I've known it all my life)
The point seems to me to be that Gunga Din was only respect-worthy once he proveded himself fearless in battle and risking his life (and losing it) to help and save his white 'superiors'. If he had merely continued fetching water and performing servant's duties, presumably they would have continued bullying and abusing him ad infinitum.

It reminds me of the attitude of my parents to their excellent dentist (in the fifties) who happened to be black. They often remarked how wonderful he was 'in spite of being a black man' (!!!) and when I was in hospital aged seven with a badly broken leg, my attention was drawn to the kindly black nurse who gently washed me. 'They' make very good nurses don't 'they'?

In a word, it's patronising.