Regarding Mravinsky's not premiering the 13th symphony, I don't know if the conductor ever spoke publicly on the issue. I recall from Wilson's book that a witness said Mravinsky was concerned not just for himself but for the well being of his musicians - doubtless the hellish years of the 1930s were still alive in his memory.
Another factor which I have not seen discussed is the first performance of the 4th symphony, a year before the 13th. The orchestral parts were discovered in the archives of the Leningrad Symphony, i.e. Mravinsky's own orchestra, and yet the premiere was undertaken by another. We don't know why this happened, but is it possible that Mravinsky was offended by his exclusion from this important musical event?
Regarding Prokofiev's October cantata, I don't think Gergiev's performance should be taken as representing this work in its best light, certainly if that performance was as insensitively rushed as his LSO one (the video is currently on youtube). In such an aggressive work, it's vital that the more lyrical moments be given their full value.
Kondrashin too was an aggressive conductor (though not as much as Gergiev at his worst). Add to this the compromised sound of the recording, and its incomplete state (two controversial movements were omitted from his complete recording). Listeners would be better off encountering this work in the Jarvi recording, or the obscure Titov (on the Beaux Authentics label).
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