Sorge’s key contribution to the war was the knowledge that the Japanese would not attack Russia in 1941, which allowed Stalin to move forces to save Moscow. Rochefort on the other hand led the intelligence effort that allowed Nimitz to ambush the Japanese fleet six months later. Both of these men ultimately lost “office politics” which led to them both being marginalized and ignored by their governments after their great victories. Rochefort ended up the better of the two, only being reduced to building dry docks, while Sorge ended up being shot,even though the Japanese tried multiple times to trade him back for their own captured spies.
One side note - it’s amazing how good and ruthless the soviet spy network was. They were simultaneously stealing Japanese war plans, hitlers sexual history, Churchill oppositions private notes and atomic designs from the US. It’s not for nothing that the red scare occurred after the war.
That's very questionable. No one knows who the greatest spy was/is.
Spies might work clandestinely but they serve somebody and as such they can not do so entirely alone as those who they serve must know who they are. Records always exist.
Over time, such things get declassified and historians can take a long, hard look at reevaluating the evidence.
Even the most small details of the Second World War are now mostly declassified, and so we can see individual contributions in the context of that war and all wars proceeding it. So, with the caveat there might be others we do not yet know about, a statement like that can be made.
It's worth remembering that history is fluid, and we have to update the facts constantly. Churchill's war diaries were taken as fact until about 1990, when it became apparent that he had lionised himself to some degree.
The goings-on at Bletchley Park were classified so well until the late 1970s, that when the first book was published about what happened there, people who had worked there still refused to talk about their experiences.
So, yes, there may be greater and better Soviet spies than Richard Sorge. However, the line you're referring to is from Owen Matthews, "his latest and most thorough biographer", and if you read the article it's clear that the book he has written is thorough and stands in the context of a huge amount of research around the Soviet spy machine in that era.
It is possible a greater spy will emerge in future, sure. For now though, the chances of another character popping up pre-1945 is pretty slim.
It should be noted that the Soviet state was very aggressive in whitewashing themselves and marring their opponents. "Who needs your damned truth if it makes our lives more difficult", one of their leaders said. Their documents should not be taken at face value.
We shouldn't extrapolate the customs of democratic societies to the rest of the world. The bulk of Soviet WW2 archives are to remain classified in Russia until at least 2040.