IMO, Fitzpatrick is at his worst, and least accurate, when he really puts a little oomph on the ball. Early this year, everything was timing patterns and he could throw at a reasonable "pace" for him. His completion percentage was fantastic, little to no INTs, etc.
Without a deep threat, teams can jam the Bills receivers all they want, and since we're running with a really mediocre WR core, once they do get off the line there's very little separation, and Fitz has four DL in his face by that point, so he's got to "force" the ball, and that's when he has problems.
If I was the front office, I'd get a couple burners who can keep the defense honest. Then I'd let the o-line get healthy. Fitz is fine when he can dictate his throws and timing on his own terms. Once you get a guy or two who can stretch the field - and get off the line - you can't cover all the underneath stuff all the time.