That was the reason for Suchet, argueably Napoleon's best general at that point, being left to defend the border.
Just in passing, no one has yet mentioned the phenomenal Marshal Brune who held off the Austrian Army from Italy with a tiny force (the Allies were so embarrassed that they murdered him when he finally surrendered).
As for Napoleon's choice of senior generals for the Waterloo Campaign, well that was to some extent forced upon him. Berthier was dead (probably assassinated by being thrown out of his own window), so Napoleon needed a good Chief-of-Staff. He chose Soult because he didn't trust Louis's ex-Minister for War enough to leave him in Paris (remember what had happened there in 1814).
Davout was left at Paris because he was the most capable and trustworthy. Marmont, MacDonald and Mortier were not available. Despite criticisms, Grouchy was a good commander, as he demonstrated after Waterloo, winning at Wavre and bringing his Wing back to France intact by a circuitous route. Ney was also good, but not as effective as he had been, especially without Jomini to advise him. But at least he was loyal (remarks about a certain "iron cage" notwithstanding).
The failure of the Waterloo Campaign is down the Napoleon in my opinion, not his subordinates. Ney was not properly briefed, joining his new command on the march north. Ney's orders were to capture Quatre Bra and push north, he needed d'Erlon for this since Wellington actually outnumbered him on the day. Napoleon failed to inform Ney that blocking the road at Quatre Bras was sufficient, and he also failed to tell Ney he was detaching d'Erlon. At Waterloo, Napoleon detached Ney's horse artillery before the famous cavalry charges, and when asked for infantry reinforcements, actually gave Ney more cavalry instead.
Grouchy was fooled by the desertion of the Saxons who looked remarkably like the whole Prussian army retreating on Namur and Liege.
If Napoleon's plan at Ligny had succeeded, then Wellington would not have stood at Waterloo, but would have instead retreated on Antwerp. Napoleon did not have time to pursue Wellington because he needed to get back to face the Austrians and Russians.
As mentioned in an earlier post, a decisive French victory at Waterloo was very unlikely due to Wellington's caution and ability to retreat, and the Prussian's resiliance which allowed them to continue fighting after heavy defeats. The best outcome for Napoleon would have been a decisive Ligny (with d'Erlon delivering the killing blow) followed by a rapid march south to pick up Davout's 125,000 being trained around Paris.
The outcome of the war would then hinge on Napoleon's ability to quickly defeat the Austrians and German Allies before the Russians arrived from the German interior. A decisive Austrian defeat was the only prospect for breaking the Allied Coalition, but Napoleon really needed another Ulm to achieve this, so I think my money would have been on the Allies.