Was lack of pass rush the cause of this historic aberration?

If you're not interested in a rehash post please feel free to stop reading now and my apologies for cluttering the board.

I realize posting at this time when everyone is angry/frustrated is ill advised, but many of us are trying to process and understand how our #1 defense served up the worst performance in the history of the rivalry.  We all want this categorized, understood and processed so we can move on mentally and emotionally. 

A simple take that might provide such understanding is that this game was defined by the lack of pass rush, period.  No pass rush exposed Michigan in 2 ways:

1. Brown's defense is unduly reliant on pass rush, without which it has glaring weaknesses.

2. Haskins is arguably the best passing QB in Big Ten history and the lack of pressure gave him time to follow Indiana's blue print and expose those weaknesses in a way only someone of his caliber could.

A talent or speed gap was not the cause. It was a defense over reliant on an element that was missing, coming face to face with the best QB arguably in generations to expose that missing element.  Can anyone point to another game where the pass rush was this non-existent in the Don Brown era?  Please elaborate on if I'm way off here but this is how I am processing this aberration of a game unless educated otherwise.

Thanks in advance for any input.