The guy cowrote Principia Mathematica AND won the Nobel prize in literature. He pretty much destroyed Frege's life's work in a witty little personal letter that could've fit on a napkin. He's one of those rare thinkers that did so much that if he only did a tenth of what he actually did he'd still be considered great.
This is a gross exaggeration, and not something that Russell himself would agree with.
----
As I think about acts of integrity and grace, I realise that there is nothing in my knowledge to compare with Frege’s dedication to truth. His entire life’s work was on the verge of completion, much of his work had been ignored to the benefit of men infinitely less capable, his second volume was about to be published, and upon finding that his fundamental assumption was in error, he responded with intellectual pleasure clearly submerging any feelings of personal disappointment. It was almost superhuman and a telling indication of that of which men are capable if their dedication is to creative work and knowledge instead of cruder efforts to dominate and be known. (Quoted in van Heijenoort (1967), 127)
I should say that I don't agree with the OP's opinion that Russell is "not great", but there's no need to exaggerate Russell's importance in order to prove it.
Not to mention that the Nobel Prize in literature isn't awarded for philosophical achievement, so that's largely irrelevant.