It's not that there weren't elements of British rule that weren't a net positive impact on some of the regressive practices and institutions prevalent in the subcontinent, it's the fact that the ruthlessness and the unsustainable manner in which some cultures and regions were united (and some divided) with no rhyme or reason except to maximise financial gain (with no thought given to the quality of life of the local populace) not only served to cause incalculable damage and conflict, it also actively undid a lot of the stability the region developed after centuries of (generally) peaceful co-existence. I certainly don't think it'd be possible to summarise the extent of the impact colonial rule on the subcontinent in one sentence, but even if it were possible there wouldn't be any version of it that went "I thought it was the British that united India".