True, but isn't there a difference between the clearance time through the tube for a missile and a shell? Would what may be stabilized enough for the passage of a shell still be sufficient for a missile throughout its boost/launch period?
There is difference in travel time, but the stabilizer works fine for it. In fact, gun-launched missiles work fine for unstabilized use too - the US used to field the MGM-51 Shillelagh missile in the M551 Sheridan and the M60A2 “Starship”.
https://en.wikipedia.org/wiki/MGM-51_Shillelagh
https://upload.wikimedia.org/wikipedia/commons/5/58/MGM-51.jpg
The Israelis have a modern missile called the LAHAT they fire out of their Merkava main guns: https://en.wikipedia.org/wiki/LAHAT