Why would the addition of some more Muslims in the North-West and Bengal stem the rise of RSS ideology? It would still be popular in the so-called "Cow Belt".
Muslims would still be a 15-20% minority in the rest of India. And we can see how politically marginalized they are today despite being 170 million strong.
Pop of Pakistan = 197 mil
Pop of Bangaldesh = 164.7 (assuming both are near 100% Muslim)
Muslim Pop of India = 201 mil
Total Muslim pop of an ATL United India = 562.7 mil
Pop of Pakistan + Bangladesh + India = roughly 1.7 billion people
562.7 mil/ 1.7 billion = around 33%
Now that is a very rough estimate, but the Muslim population in this new India would
at least double OTL India's Muslim population. You cannot say that that would not have an affect on India's politics. And it isn't, as you say, "some more Muslims in the North-west and Bengal", this is completely changing the recent history of some of the most populous and affluent provinces in all of India. An unpartitioned Bengal and Punjab would have immense influence on the national politics of an ATL India, and not to mention the Muslims that left from the central provinces. Listen, I understand why a lot of people get the impression that Muslims and Hindus (specifically Indians and Pakistanis) have and always will have an undying resentment for one another, but that hatred is the result of the bloodshed and horrors of partition, several wars and territorial disputes, and seething tension over Kashmir. These things have all occurred as a result of the British doing a shit job at leaving the subcontinent in peace, and the fact that some Indian independence leaders who could not foresee what their squabbles and disagreements over Indian independence would cause. In summary, with all the economic destruction, political and social tension, and instability that partition caused, there is absolutely no way that a united India would not be better than what we have today.