I strongly feel stereo sounds better in 90% of the venues..
The lone exception is an audience within 180 degrees of the speakers[a hard right and left of speakers]..
True from a long distance the stereo image is greatly reduced...so what, why sacrifice the stereo in the range that will sound great..People that sit in the back of the room, will hear mono...others will hear stereo..
Some instruments that always seem to sound better in stereo[even in the back of the room]..are drums..fills and crash cymbals seem to be more live..Also separation of individual instruments like a guitar on one side , and a sax to the other side..add dimension..
As I mentioned there are 10 percent of the rooms that mono is more suitable......and my winter gig is one of those..