Mukti Bahimi members has been receiving training in India long before any thing between Mujeeb and army had gone south, long before the elections were held. Awami party has been sending soldiers across the border in India to receive military training alongside Indian army. While the soviets conducted propaganda and psychological warfare. It was the reason why Pakistan army was irked, mujeeb was playing a double game. If you ignore the propaganda and study the issue unbiasedly you ll certainly come across the truth.
Even tho Bengalis were undoubtedly marginalised by west Pakistan which is true and yahya was a terrible ruler, it would be incorrect to say that the events unfolded only in the last year during yahyas tenure. Mujeeb has decided on separating long before.
I would recomend you reading Yuri Bezmenov’s book on psychological subversion where he’s clearly mentioned what happened in Dhaka.
what your basing your argument on plain indian and Awami league propaganda so I’d advise you research unbiasedly to find out the truth.