Mother Russia is not a good song, tho.
I disagree with this and your conclusion. It's a good song that suffers a lot from the poor production of the album. Obviously, it doesn't convey the sense of majesty and pomp they were going for, but it's still a good composition and decently performed. We can only speculate why it wasn't played live, but a lot of songs the band liked had poor live treatment. But I don't think we can take this as proof that it's not a good song anyway.