if he didn't want to be emperor (perfectly understandable) he shouldn't have signed that GDs manifesto agains Nicholas. Since the manifesto clearly required the abdication of Nicholas to have Michail as a regent.
The GD's manifesto he signed (after GD Pavel and GD Kirill, was that one proposed a new constitution, creation of constitutional monarchy after war and formation of a new government. Michael indeed signed that, and then, when it ceased to be relevant, he asked to remove his name. But it was not a manifesto against Nicholas.
I'm quoting from The Fall of the Romanovs, page 87 - 91. On page 90 appear 3 request of abdication for Nicholas. One from Nikolasha, the second (the one i'm referring to) from General Brusilov. This latter clearly writes: "I ask you to report His Imperial Majesty (...) to abdicate the throne in favour of His Majesty's Heir tsarevitch with Grand Duke Michail Aleksadrovich as regent."
You are quoting not a manifesto, but responses sent to Pskov by commanders, when Nicholas was still not sure - to abdicate or not. The commanders advised to abdicate.
What i meant is: did Michail know of this request? i can't say for sure, but it's likely since he signed the manifesto. So: IF he knew, and agreed, he acted IMHO like a coward because he firstly accepted this request and then, when Nicholas called him to reign (and so following that precise request) he refused. First he agreed and then was scared and refused. And this would be very odd.
Not if situation could change dramatically from one hour to the next.
But anyway - when Nicholas signed his abdication in Pskov, Michael was on Millionnaya Street in Petrograd and he had no idea , what his brother decided to do after his first abdication in favour of Aleksei (with Michael as a Regent) - that he had abdicated once more
("Not wishing to be parted from our beloved Son"). Michael didn't know that he was new Emperor until Friday, March 3, probably when the delegation of Duma came at Milionnaya St. to meet him.
So when he signed GD's manifesto (which should also sign Nicholas after his return to Petrograd), he didn't know about his brother's decision. Actually when exactly he agreed to be a Tsar? He was told suddenly that he is already a new Emperor, nobody asked him whether he wants it or not. Letter of apologizes (for this unexpected "suprise") from Nicholas to his younger brother not reached the addressee.
It was said Michael let himself to be persuaded to give up the throne - but in fact his manifesto is not the abdication
("I have taken a firm decision to assume the Supreme Power ONLY IF such be the will of our great people") . It was not his fault that there was no universal suffrage and soon after the power had passed into the hands of the bolsheviks.
If the situation in the country after abdication of Nicholas II was different, Michael could be a good constitutional monarch. But as you said, Sunny, it is only "what if"...
There were many cowards in Romanov family, there were even a traitors (like was Kirill Vladimirovich in my opinion), but to call Michael
'a coward' it is just injustice.