I personally wouldn't read too much into the quote just yet.
The quote regarding Birmingham is not anything from AI itself, but the opinion of the author, who has an obvious bias towards BHX due to his previous role (and as good as admits that bias).
In his dismissal of MAN, he has totally overlooked the fact Delhi is AI's main long haul hub, and Delhi on its own has a larger demand to MAN than BHX.
Don't forget though, this is Air India we are talking about, the obvious choice isn't always the choice they go for....