Nivelle was the product of a general failure to realize that the classical offensive model was not going to work on the conditions of the Western Front. It would be necessary that the French learned the right lessons from Verdun, rather than foolish ideas of all conquering artillery fire. And with the US entering the war, the realistic aproach should have been to keep up the pressure until the US forces were in France in large battle ready numbers rather than seeking decisive breaktrough battles. Nivelle demonstrated that the French had learned nothing from their own failures in 1915 and from the british failures in 1916.
I would have liked to see Petain handling the whole of the French army in the way Gen Plummer handled the British 2nd Army, with careful planning, concern for morale and realistic tactics. This may be asking too much, but Nivelle did so badly it would be difficult not to do better...
And the general prejudice against Petain resulting from his WW2 record makes him a rather unpopular alternate choice for CO, but he might have been the right man in early 1917.
Nivelle was much more than that; he was a monster
his idea was to launch a pincer attack against the saliant... fine enough in theory
BUT poor operational security by himself and his staff saw the plan being talked about in the chamber of deputies and in cafe's in paris, which necessarily leaked it to the germans
the germans then evacuated the target salient; leaving a dead zone in between covered by pre-registered artillery and dug into the 1917 unbreakable hindenberg line, rendering the entire concept of the offensive pointless
Nivelle moved up into the death zone, which saw his assembly areas being constantly harassed by german howitzers enjoying higher ground
His subordinates where dead sure the offensive couldn't succeed under the new real circumstances and cried foul to the politicians; but only Petain had the balls to say that even if they broke through that they didn't have enough reserves to advance, but that he didn't think they could break through anyway
Nivelle, cornered like the coward and idiot he was, threatened his resignation if he could launch the suicide attack, the government, realizing they would fall if Nivelle left, also took the cowards way out and let it go forward, the only caveat being that if the offensive didn't break through in 48 hours it would be stopped; yet Nivelle was allowed to send more than 30 thousand frenchmen to their deaths over three weeks with many thousands more wounded until the army had to mutiny to defend itself