The state of the British army was poor as well.
But not so poor , I think
. The overall quality of British infantry was the best in the world in those last Napoleonic years; the French Imperial Guard only (the Old and Middle Guard) could have been better; but the overall quality of French infantry at Waterloo wasn't so good as the British; certainly French infantry wasn't the same infantry who fought at Austerlitz!! About the Cavalry, I think the French one was better, but the British Cavalry was not so bad, after years of practice: in 1815 British horsemen were experienced (and they had very high quality horses). About Artillery, yes, the French one was incomparable, mighty, the British one good but without "excellence", I think.
The low morale of the Army and the Nation was an important cause in the defeat of Napoleon; but my opinion is the French made lot of mistakes in the Campaign and in the three main battles (the Allied too, but less). One mistake above all: the behaviour of Grouchy! If Grouchy have had fever
and could not have been in command the 18th of June, I could say that EVERY general (not necessarily the great Davout) had marched towards the "sound" of the firing guns, so the French had won the battle!