I've always thought that McKenzie was a really good spot player. Put him in the game to add some mystery to the offense. Might be a gadget, or just another wrinkle to an already lethal short passing game.
Unfortunately, the "Peter Principle" caught the Bills apparently by surprise. Isaiah earned a bigger role, especially after last season's NE game. But, he earned a bigger role that he simply is not capable of. Whether he loses focus, concentration, or just can't handle the additional responsibility, McKenzie seemingly just loses his way.
I am not a proponent of cutting him, as some here have suggested. He is still a wonderful spot contributor on offense. It is abundantly clear to me that he is just not capable of carrying the load required of a starting slot guy on a championship caliber offense. He's been around awhile now. He's not going to change much from where he's currently at. After his game yesterday, I have to believe that the coaching staff has also come to that final realization.
Like so many others before him, Lil Dirty will have to be content with spot duty as a role player moving forward.