It is debatable whether there was an evil plan or situation just unfolded as it is after independence. I would say its later, punjabis are still dismissive about bengalis, and if you watch the leaders of west pakistanis(old video footage) they were same.
What you are saying is, because bangladesh is heavily influenced by India now, everything was ok back then. Thats simply not true, you cant fool millions of muslims in bd, they are not all stupid. The overwhelming support was for self-determination(if not independence) and pak govt action just made it easier. Instead of trying to win bengalis by doing political deal with their leaders, they tried strong arm tactics. I am sorry you ended up being on losing side, and India takes some of the blame but not all.