surely one of the greatest Russian composers since Tchaikovsky
Hmmm, I saw what you did there ;)
Quite a few rather important composers have slipped through the cracks there, haven't they?
Both Taneyevs (although primarily Sergey), Rimsky-Korsakov, Gliere, Glazunov, Scriabin, Rachmaninov, Medtner, Prokofiev, and a chap called Stravinsky? Not to mention a host of piano-soloist-composers, and other composers from the non-Russian parts of the USSR, and even further afield.
I think there are strong grounds for naming Prokofiev as another worthy carrier of Tchaikovsky's mantle? He lovingly pastiches his beloved master in so many of his works, WAR & PEACE not being the least of them (which opens with a clear homage to THE QUEEN OF SPADES)
Ah, well - as long as you saw what I did there(!). No, none of those composers has slipped through any cracks, of course (and, speaking of cracks, perhaps the joke backfired somewhat, but at least the statement got a reaction!) - and even then, I did write "one of"(!) and it hardly needs saying that Tikhon Tikhov falls far short of meriting includion therewith. There's Gretchaninov, Roslavets, Weinberg and others too..
The serious point behind that statement was, of course, that Shostakovich is one of the 20th century Russian luminaries (even the egregious Abraham mentions "common consent" and is not without his compliments about Shostakovich - yes, I made myself trawl through as much as I could stand of his essay on the composer) - but that, among British music critics, Abraham is (deservedly) hardly remembered today, even in his own country. What Abraham he forgot (or more likely didn't know) is that Shostakovich's first symphony was not just a conservatoire student piece; he began working on it a good 2½ years before he completed it.
That said, I see little point in dignifying his ill-considered statements about Shostakovich with further discussion of his essay, except to mention
en passant that even he seems to have a considerably more positive view of the composer than does Gerard.