I think you are overstating the case a little, JAG. Didn't Napoleon himself say something before the battle was decided about Blucher's approach swinging the odds significantly against him?

In most wargames, Waterloo appears a "fair fight" without the Prussians: the French have a slight advantage in numbers but the English have position and the luxury of defence. I personally think the English have the edge if follow Wellington's tactics and the French follow their usual Napoleonic tactics - it seems always thus, whenever they met. However, it definitely becomes an uphill struggle for the French when the Prussians are included.

On the day, the Prussians crushed the French right and had driven into the rear of Napoleon's position (Placenoit?) by the time the French made the decisive attack on the Anglo-Dutch army with the Guard. I suspect the repulse of the Guard started a rout not so much because the French thought the Guard could not fail (the usual myth). But instead, the French panicked when they realised there was a second large aggressive enemy army right in their rear. (by analogy MTW captures the morale effects of enemy cav in your rear pretty well).

Without the Prussians, Napoleon could have taken a little more time and exploited the seizure of La Haye Sainte with Lobau's Corps and the Guard. Who knows, maybe Napoleon could even have pulled off a Prryhic victory (despite having had the rest of his army badly mauled earlier in the day)? I suspect it might have been more like another Quatre Bras though - pretty much a draw.

In the bigger pictue of things the 100 Days campaign was pretty hopeless though - the Allies had masses of manpower mustering to crush France. The Allies were collectively determined to see the thing through and also had able commanders who had learnt enough from Napoleon not to be cowed by him. By contrast, France was exhausted and internally rather divided. I doubt there was anything Napoleon could have done, even at the height of his power, to win in the end. He gave it a pretty good shot, but Wellington and Blucher just resolutely beat him down.