Please excuse my late arrival in the thread. If you can't tell the difference between a mono and a stereo recording of something, and the "something" took place in a space with a more or less normal amount of reverberation, then the stereo recording isn't optimal to my way of thinking.
I, too, have used one-point Sony stereo microphones in decades past (and also some Aiwas, which were less peaky in the treble), and even if that's not quite the ideal way to record stereo, it still can be better than mono. And the convenience factor sometimes means that a recording can be made under circumstances where no other form of recording is practical at all, so I don't knock that, either.
The thing is, many of those little stereo microphones were really designed for business applications, e.g. recording a meeting with ten or twenty people sitting around a table or a room, so they tend to have a very wide stereo pickup angle. And the way this was (and still is) often done is by arranging the two cardioid capsules with an angle of only 90ยบ or so between their main axes. Cardioid isn't really all that "sharp" of a pickup pattern, so when you use the mike in other, less immersive situations such as concert recording, you find that there's a tremendous overlap between what the two channels are each picking up. In fact their signals turn out to be so nearly alike that the resulting two-channel recording is pretty nearly mono in effect.
And that, in turn, may well explain why a reasonable person who listens to the recording over loudspeakers might not feel that stereo has much to offer over mono. But a more appropriate recording method should show the advantages rather vividly, I think.
--best regards