Most of the units you speak about were to be found in the 4th Corps in 1813 and indeed came from Italy and were largely units that had a strong core of veterans along with conscripts that had been induced in 1811 and 1812 so those regiments were usually more competent than most if not all of the 1813 Army. Besides those most of Macdonald's men of the XIe Corps were veterans from 1812 in Russia so hardy and tough veterans for the most, hence the great difference in bayonet strengh between them and the usual frenc battalion formed in the late winter of 1813 - 400 men for the usual 7 to 800 hundred.

After the losses incurred in the 1813 spring battles it is more than certain that even those regiments received a large number of conscripts to refill the ranks thereby reducing their average quality for the autumn campaign. I would say that Napoleon's problem in 1813 was not so much in battlefield capability, except maybe in the cavalry but much more in strategic mobility and morale where the french troops were consistently poor. Troops under pressure on retreat would disband quickly and when confronted with lack of success or utter defeat most of the losses would occur during retreats. It is a sympthom of low morale and stamina for me.

Cheers
Mathias