ts, I'm fairly certain that I'm as old and (sorry to say) as farty as anyone else around here, and I believe that a person will probably make the best recordings with the mikes that he or she is the most familiar with, whose behavior makes the most sense to him or her. I would never try to dissuade you from using shotguns for stereo music recording if they've worked well for you and their behavior fits your expectations.
But I would never advise anyone else to take up that path. All other things being equal, good recordings are far more likely to occur with microphones whose frequency response is as similar as possible across the main angles of sound incidence, or whose directional pattern remains fairly constant across the audio frequency spectrum (which is actually the same thing, viewed from a different perspective). And shotgun microphones are designed from the start to be ... not that. They are designed to reduce the pickup of off-axis sound (which, if they're aimed skilfully, will always be reflected sound) in the frequency range where spoken consonants mainly occur, so as to increase the intelligibility of speech pickup when the miking distance is a little greater than might otherwise be ideal.
That said, you hit the nail right on the head about short shotguns. Most audio professionals who use shotguns will choose a short shotgun over a long one if the directivity of the short shotgun is sufficient; it sounds better, and in applications such as film and video sound, generally lets you get the transducer closer to the sound source. But most audio professionals will also choose a good supercardioid over any kind of shotgun if the directivity of the supercardioid is sufficient, for the same reasons.
The explanation for this is the relative evenness or unevenness of the directional pattern across the frequency spectrum. A good single-diaphragm supercardioid such as a Schoeps, Neumann or Sennheiser can have a uniform directional pattern from the lowest audio frequencies throughout the entire midrange, narrowing only in the top octave-and-a-half or so. A long shotgun, by contrast, will have (usually) a supercardioid pattern at low and low-middle frequencies, narrowing through the midrange/upper midrange while also developing considerable irregularity in its sensitivity to sound arriving at various angles.
This effect becomes more and more severe the higher the frequency in any shotgun microphone, and the longer the tube is. Thus a short shotgun (a) retains a consistent pattern up to a higher frequency than a long shotgun, and (b) has less severe irregularities in its sensitivity at various angles once its pattern does begin to become narrower. This is the main reason why the best-sounding shotgun microphones are invariably short.
--best regards