Well, I didn't leave but I will second your friend's sentiment. This was indeed the worst sound, by a long shot, that I ever experienced at a Dead show. I recall the only exciting moment being the mid set Iko.
I was even with the soundboard about 1/2 up the lower section, so not great not not exactly horrible seats. There's an FOB Schoeps tape that sounds at least somewhat passable, so the sound was apparently better in the sweet spot. But still. Horrific venue and a totally flat show.
Santana opened, and this was the only show I ever saw where the opening act outshone The Boys.