Ney was a perfectly competent (though definitely aggressive) commander. Friedland is definite proof of that. It's just that, among the Marshals of the First French Empire, he was greatly overshadowed by giants such as Lannes, Davout, Massena, and Suchet. I would also personally rank Marshals such as Bessieres, Jourdan, and St-Cyr his superiors as well. His performance at Waterloo was certainly not his best, it can be said.
If there's anyone you can criticize for handicapping Napoleon (I suppose you mean in Waterloo), it'd be Grouchy. A perfectly good cavalry commander, he just couldn't operate in an independent fashion (noted by his failure to both defeat/delay the Prussians or join with Napoleon at Waterloo [when in doubt, you should always march towards the sound of cannonfire, which Grouchy did not]).