Low deviation isn't entirely good, it is actually a can be a sign of bad voting as much as good.
Curation snipers typically drop low votes on many authors for the best chance of curation rewards. Many of the curation snipers drop $0.00 votes to get 8x the curation reward of the typical user. It is fairly common to use the same weight votes (appreciator, for example, votes 9-12% 99% of the time, and curation snipers voting 0-1% most of the time with no specific favoritism as it is just sniping as many posts at ideal times as possible).
In the case of some of the largest "curators", it is a different problem, finding posts with little rewards and voting them very late to get near 100% curation. But it uses the same technique, large amount of similarly sized votes, none of them based on quality.
Both of these types of "curators" will perform well on these charts (and do).
RE: Ranking the Top Curators on Hive | Number of votes, authors, vote diversification | The reward goes to ….