The 90s teams were at least competitive. In 1990, they were either the second or third best team in the conference. In 1992, they were likewise a legitimate SB contender. 1994 as well. Almost certainly those teams lose in the SB, but the late 80s teams couldn't even make the playoffs. The JJ teams were barely playoff teams. And they were at no point legitimate contenders. They were badly, badly exposed in the second round. The 90s Shula teams didn't go down without a fight in the first two rounds (except that 1995 team that got blown off the ball in Buffalo). The 1992 AFC championship was mighty disappointing though.
That said, I nominate 1991 as one of the worst seasons under Shula. That was a team poised to make a move after 1990 and they go a pathetic 8-8 and let the lowly Jets beat them at home to take the final playoff spot.