That the top kill might have worked if it had been tried longer?
Perhaps, but the problem was overcoming the massive flow prior to getting a column of mud deep enough into the casing to gain enough weight to stabilize the pressure.
It took a much deeper point of intersection that resulted in a much heaver, longer column of mud prior to penetrating casing nearer the field depth.
With the information I have seen, I doubt the top kill would have eventually worked, but it was possible and certainly was worth trying.
Well, much of what was tried down there was a long shot and it worked. No one was betting on that dispersant working as well as it did.