Well yes and no, that 30% was during a high-point of the Mughal empire and before the widespread development of industrial capitalism. Its certainly the case that Indian society may have turned out differently if not for the British, but maybe not for the better, it was a society descending into factionalism and civil strife as that empire collapsed, the British simply stepped in and took over primarily to secure their trade interests, because they couldn't trust the local kings and warlords to do so anymore. In doing so, and then later establishing a government, they introduced modern medicine, education, roads, the rail network, and other critical infrastructure, as well as industrial capitalism.
This is not to excuse the British, but perhaps India would've been better off without them, perhaps not, the alternative, if there wasn't a single government, could've been a patchwork of dysfunctional extractavist states, like what you see in Africa. It may have been possible for a large south asian society to organize itself in an egalitarian fashion, but unless some miracle happened they would've been overrun by foreign capitalists, who had far more power than any other class in history, because South Asia is incredibly labor and resource rich, and at the time the only parts of the world that had even developed industrial capitalism were in the "west", Europe and the US, not to mention the only place that avoided that fate, Japan--the latter being moreso an exception that proves the rule (and which, after all, turned fascist during WW2).