ahead of the all-time great defensive centers like D. Robinson, Dikembe Mutombo, Ewing, Eaton, etc. So to say that this listing should be taken with a grain of salt is a bit of an exaggeration.
Stating that "a lot of people estimate Russell would have more" as evidence that Russell would have had more, is much more of "a grain of salt" then actual numbers that show Hakeem has 500+ more than anyone else since it began to be tracked.
So at worse, speculatively he is number 3 on the all-time block list? Doesn't really change the point that I made.
I will grant that there is a chance that Russell and Chamberlain would have had more blocks, but that it wouldn't mean much in reality. Russell and Chamberlain both have exaggerated stats in large part because of the pace of play during their era. Teams put up a lot more shots per game during that time. More shots equal more rebounds (and thus their inflated rebounding numbers). More shot attempts would likely equate to more block attempts and more blocks.
My point is, even if Russell did have more blocks, it wouldn't necessarily be proof of anything other than he played in era that provided more block attempts. While Hakeem played in the same era and at the same pace as the other all-time greats, thus making his stats all the more impressive and distinguished from his peers.