I don't think it was an issue with scheming him open, I think it was when Brady took over, that they stuck to the run game...and it paid off in a big way. Ran for at least 100 years every game the rest of the year and there was a direct correlation between Diggs decline in production and James Cook and the run games increase.
More than anything, the Bills were just kneecapped with the salary cap.
"The salary cap has never prevented a team from signing a player, poor personnel decisions have."
-Andrew Brandt
Von Miller's contract extension was one of those deals. Dawson Knox, Milano...but more than that, they've had some huge injuries(White in back-to-back years) and poor drafts since Josh Allen. Also traded Wyatt Teller, an AP caliber Guard, a position of weakness for them for years after for a short term fix.
They did what I would hope Gute doesn't do, and that was go all in to win the SB with a young QB. We saw Gute do that with Rodgers...but that made sense. The Packers will hopefully thread that fine line between being aggressive and going for it...and playing it too conservatively with a young(hopefully) Star QB.