Finally my opinion on some very dominating saimoe contestants and the overall chart.
I would like to divide the saimoe history in few periods.
Period "0" - before AST
It seems only a minority of the early saimoe tournaments dealt exclusively with anime characters. Other saimoe tournaments focused on visual novels, games, manga or music. The earliest saimoe tournament I could find (through http://web.archive.org/web/200402030351 ... emain.html
) was the Leaf Key board saimoe tournament ("葉鍵板最萌トーナメント") which started in October 2001: http://web.archive.org/web/200402030351 ... emain.html
Period 1 - early AST era
I would include the first four editions of AST (2002 to 2005). It started as a 6-month long tournament and in 2005 Takamachi Nanoha was probably the first champion internationally known. I found only few other tournaments - all Japanese (2002 GAINAX Saimoe Tournament, 2004 World Masterpiece Theater Saimoe Tournament and 2004 Tōhyō Anime Saimoe Tournament).
Period 2 - "classic" era
I would include the next five editions of AST (2006 to 2010). A lot of epigonic saimoe tournaments started all over the world: Korean Best Moe and Super Best Moe, Yamibo Yuri Saimoe, Chica Anime All Stars, PTT C_Chat Saimoe, loli battle, ISML, Animefans Saimoe Tournament, Baidu Harem Moe or TGBUS Chinese Saimoe.
Most of the saimoe tournaments/communities shared a common taste. You can watch the video and see how many characters got many points (especially after ISML started in 2008). The best example may be November 2009 where three characters had more than 1000 points each and a fourth character had more than 900 points. This was only possible since they were successful in many tournaments. Apart from the three double champions (Suiseiseki 2006, Aisaka Taiga 2009 and Akiyama Mio 2010), I have to mention Hiiragi Kagami (champion AST 2008, 2nd place KBM 2009, 3rd place ISML 2008), Katsura Hinagiku (champion KBM 2007, ISML 2009, semifinalist AST 2008) and Shana (champion KSBM 2007, 2nd place ISML 2009, KBM 2007, semifinalist AST 2006). I would say characters from Kyoto Animation and J. C. Staff animes dominated this period.
And why was Shana so dominant? Being a tsundere loli helped, of course, but more important was, in my opinion, the lack of competitors in her own series. Looking at the tournaments we can see Rozen Maiden dolls fight each other, many strong CLANNAD characters, but none of them won a major tournament and the battle inside the SOS brigade. Katsura Hinagiku had a long rivalry with Sanzen'in Nagi and I guess some Hayate no Gotoku fans thought "Hinagiku is the best girl, but Nagi is more moe" which prevented Katsura Hinagiku from being the dominant girl of the period.
Period 3 - transition (or schism) period?
I would include the last four editions of AST (2011 to 2014). I think there are three tournament related events that justify starting a new period in 2010/11:
(1) The first of the epigonic saimoe tournaments disappeared: loli battle (last edition 2008), TGBUS Chinese Saimoe (last edition 2009), Korean Super Best Moe (last edition 2010) and PTT C_Chat Saimoe (last edition 2011). This marked the end of the first "saimoe boom period", although new saimoe tournaments started as a compensation (Baidu Anime Saimoe Tournament, Senpuu Saimoe Tournament, and lot of facebook tournaments).
(2) The strong dominance of K-ON! in 2010, winning all major tournaments (plus Aniparty Saimoe and PTT C_Chat Saimoe) and claiming the first and second place in the Best Waifu Rating.
(3) Two multivoter involved incidents in the major tournaments in 2011 lead to a schism in the saimoe community, as I would call it. First Misaka Mikoto and Tachibana Kanade were eliminated in AST group finals after their fanbase had been accused of multivoting in earlier matches. Later KBM was stopped during group finals after Kasugano Sora had defeated Kaname Madoka thanks to multivoters. The tournament restarted from round of 96 again. Voter restriction intensified in both cases.
Afterwards AST and ISML communities disagreed on favorite characters and even favorite series. AST became dominated by Madoka and Saki factions which were also powerful in YYS and in later editions of BAST (the latter two preferred Love Live! later). Akemi Homura also won KBM 2011 and two series mates entered the quarterfinals.
The dominance of K-ON! did not occur in saimoe tournaments only, but in terms of sales too. Therefore other anime studios adopted their moe elements leading to more series with moe characters able to fight for saimoe titles. Gigguk made a good youtube video on "The Moe Anime Revolution" (https://www.youtube.com/watch?v=E1x1RicXFMk
). The interesting parts are "The Rising of Kyoto Animation" (start at 6:48) and the next chapter "The Moe Genre" (start at 12:53).
And so the influence of K-ON!, the schism between ISML and AST and the end of KBM lead to more competition and lower number of points for the top characters (no character with more than 1000 points between March 2012 and December 2013).
And why was Misaka Mikoto so dominant (reigning 34 months until June 2015)? I cannot provide a comprehensive answer. She is, like Shana, a tsundere and has, like Shana, no real opposition from other series mates: Index's saimoe popularity faded at the time Misaka Mikoto's began to rise, Shirai Kuroko was most successful in Yamibo Yuri Saimoe and Last Order is literally a clone. Her biggest advantage is winning her uncountable tournament titles over a long period of time. (Compare to Akiyama Mio who won KBM and ISML in the same month and set the global record of 1471 points. Afterwards she lost the points almost without resistance and dropped out of the top ten forever after 18 months.) I think the loyalty of her fanbase is another important point. In general, I would say saimoe communities tend to be very loyal to their favorite girls and series. (How often did Haramura Nodoka qualified for the AST quarterfinals? Four times. How often did Tachibana Kanade placed among the top three of ISML? Four times.) And her fanbase helped her to compete in many tournaments until she won them, finally. (See Animefans Saimoe Tournament: 2010 second place > 2012 quarterfinals > 2014 champion or Baidu Harem Moe: 2012 semifinals > 2015 champion or Best Girl Contest 2014 round of 32 > 2015 quarterfinals > 2016 champion).
Period 4 - present period? (Rem's reign)
It's hard to define a clear starting point for this period. I would say the end of AST 2014, the start of BGC 2014 and BILM 2015 and exclusion of past (Stella) champions from ISML after 2014 are the most important tournament related events between the two periods.
BGC and ISML are open to characters regardless of their last anime apperance (in contrast to AST and KBM). Both tournaments (and other smaller tournaments like AnimeGirls Saimoe Tournament or HK Golden Saimoe) allowed to boost nostalgia characters like Aisaka Taiga or Shana. The exclusion of past champions in BGC and ISML terminated Misaka Mikoto's reign as Best Waifu, because she couldn't get enough new points after winning BGC 2016.
Rem's reign is exceptional on the other hand. It's unique that she was able to win all major tournaments (BILM 2016, BGC 2018 and ISML 2018) and two 300 maxtp tournaments (Aniplus Character Tournament 2016 and Baidu Harem Moe 2019).
I can't say much about this period for now.