That’s a flawed argument. Elections don’t work on absolute numbers in that just because the Muslim population would have been 40% that you’d see around the same percentage of Muslim supported elected representatives.
The distribution of votes in each constituency is what determines the outcome and Muslims in India are spread out too much to influence elections. The Muslim vote in Pakistan & Bangladesh would have similarly been diluted since millions of Hindus, Sikhs & Muslims would not have migrated. So the net impact of this ‘40% Muslim vote in United India’ would have been much, much smaller than the absolute numbers of Muslims in United India, and this whole ‘Ghar Waapsi’ Hindutva BS would have been just as vicious, if not more.
Jinnah saw the writing on the wall long before anyone else. The underlying geographical demographic distribution of the Muslim & Hindu populations of a United India and the underlying religious tensions and especially the underlying Hindu insecurities and anger over Muslim rule were never going to allow a ‘secular’ Federation in the long term, especially when even the Congress party (supposedly the more secular of Indian political parties) rejected Jinnah’s idea of a Federation with significant autonomy for Muslim majority areas.
Indian Hindus can’t even tolerate a tiny number of Muslims in Kashmir exercising autonomy (see the widespread support for revocation of Article 370), let alone tolerating autonomy for vast swathes of Muslim majority territories that today form Pakistan & Bangladesh.