[RestlessMind]

(as an Indian, who has studied a lot about Indian history)

> A few tens of thousands of British troops

A lot of Indians happily joined British army because of the (relatively) better pay and better treatment.

> slaughtered by the hundreds of millions of Indians

But those were all divided into hundreds of kingdoms. In fact, a lot of Indian kings and princes preferred being a vassal of the English crown because the alternative was much worse (being imprisoned or killed by Indian rivals). Read about almost any major Indian wars/battles in the 18th century involving English and you will find a lot of neutral Indian parties, or the ones actively fighting on England's behalf.

> any half decent uprising would have been successful

Indian subcontinent suffered from a "coordination problem". Gandhi is admired because he played the biggest role in bringing a lot of them together. Of course, he couldn't bring everyone along (eg. Jinnah and Muslims), and there were a lot of other great leaders who also contributed (Patel, Tilak, Bose etc) towards uniting all the Indians, but none could attain Gandhi's stature.