Beats me how anyone can come up with these ridiculous statements about mono being superior to stereo, when actually TESTING your statements is so bone-stupidly easy...
Get a favorite CD track. One you are familiar with. Import it into an audio editing program (don't need a fancy one). About every 30 secs or so, select the audio and apply a 'MONO' preset for about 30 seconds. So you'll have a track that switches back and forth from stereo to mono, but doesn't change amplitude (the ears are VERY sensitive to small changes in amplitude).
Now, set up a stereo PA, or play it through your home stereo. Walk around the room. Listen to the track. Can you hear when it changes from mono to stereo from anywhere OTHER than the 'sweet spot'?
You bet your sweet a$$ you can!
Until you are playing rooms SO LARGE that reflected sounds overpower direct ones (and how many of us play those?
) you are going to get SOME stereo effect from anywhere. Is it going to be as good as the 'sweet spot'? Of course not... But it is certainly a LOT more than no effect at all.
Before you make blanket statements about audio, it's best to actually CHECK your assumptions...
Now, this doesn't necessarily answer whether one or the other is BETTER for a particular venue or person, but you can easily check the fallacy that there is no stereo except in the 'sweet spot'.