Well, Most of the commanding officers of East Bengal regiment mutined long before the declaration by Major Zia. Nobody sit idle or infact it was impossible to sit idle. Major Moinul disobeyed order on 19th Decembre and till that date Gazipur cantonment was under Bengalis control. They captured all the west pakistani soldier and officer kept them captive. The situation was same everywhere. Even the police/epr who was not under West Pakistani command which is why they put up resistance on the night of 25th March. Nobody knew about Zia before 27th of March.
Saying so I am not undermining Zia but Zia or not Zia, war already started on the night of 25th of March.
1) I could not more disagree with your opinion. You are talking in a political line here. People like General Subid Ali Bhuiyan of Comilla and others came out of their stories at a later time. Major mainul's action was also not known to other Bangali troops. Mainul should have come out of his hide out and fought the PA troops in Dhaka. If he had done so, he would have taken the place of Ziaur Rahman.
2) Major Mainul and others' actions were only unilateral actions and all such individual actions required unity and cooperation with each other through a single command and by setting up the final goal. The single command was absent because Sk. Mujib had not OFFICIALLY (ceremonially) proclaimed the independence of Bangladesh. It is the truth and it is the history.
3) However the Awami Leaguers try to change the history they will fail in it. AL is always worried that the Liberation War Proclamation has been unfairly hijacked by Ziaur Rahman, who was not a political figure. But, the reality is, AL itself tries to hijack the credit from Zia.
4) PA troops had already killed many hundred Bangali troops and Police in Dhaka and Chittagong (as far as I know) and other places where they were numerically superior at the very early stage of crackdown. In many of the garrisons Bengali troops were kept free but were unarmed for fear of a revolt.
5) The TIMELY declaration by Zia was itself a COMMAND on behalf of Sk. Mujib. It helped these troops to come out, fight the PA, and liberate the country. The proclamation could have come from any Bangali Officer, but history says it was Zia who did it.
6) Bangali troops were eager to revolt, fight and die, but political leadership was busy sweet talking with Yahya Khan and were dreaming how to divide the power spolis among themselves. Except SM none of them was brave enough to fight a war against PA. It was basically Bengal Regiment, Police and Ansar troops, who really fought. Unfortunately, SM was arrested unprepared, believing in the words of Yahya Khan.
7) Sk. Mujib himself was not favouring an outright independence at that particular time. He was probably thinking of repatriating the assets that have been taken away to the west at the expense of the east once he becomes the PM. That may be one reason that why he refrained from declaring one. But, the Bangali troops were too eager to sacrifice their lives to win an outright separation. So, Zia's declaration filled the vacuum.
8) What could have happened without a declaration either by Zia or any other Officer is anybody's guess. Lacking a command, individual military, Police, EPR and Ansar units would have been surrounded and wiped out easily by the united PA troops. Resistance would have been fruitless without them. And surrender would have been meaningless because PA troops would have killed all of them at point blank.
9) In such a situation, an armed liberation war could not have have continued without the Bangali PA troops at the core of the fighting. People should not expect winning a war with only civilians taking part without being trained and guided by these experienced Bangali PA troops. People's moral would have collapsed at the death of these bangali troops by the PA troops.
So, Major Zia's contribution to the 1971 war was more than many AL leaders' combined contributions. Zia will remain at the heart of the people of Bangladesh because he had rescued this country not one time, but two times. In both the cases he played a vital and pivotal role.