Also India had indeed a centuries long fighting tradition of British military service. This was not a nation of pacifists.
I think the situation was more complex. Rather, proportionally small numbers of select Indians had a long tradition of service to the British Empire. These particular Indians could then be sub divided into truly deployable, long standing, "Category A" battalions with reputations for excellence and other less reliable Category "B" battalions that were not truly deployable beyond para-military police duties. Potential Category "C" units comprised of Indian conscripts could be even more problematic.