RE: Rankings
If we just cover the time span when the beatdowns began:
The Martina N/Pam Shriver beatdowns (29 straight) were from 1982 AO (then played in Dec) 1982 through the 1992 San Antonio WTA tourney (March) which would be about 9 years, 3 months.
Chris Evert/Virgina Rizici (23 straight) was 1974 FO (May) to Hilton Head 1985 (April?) for a period of 10 years, 11 months.
Serena beat Maria in the 2005 AO(Jan) and now in the Wimbledon SF (July) so that is a period of 10 years, 6 months.
I think Virgina R. was a Major winner (FO one of the years Chris didn't play because of WTT).
The Serena/Maria beatdown is unique because Maria is a 5 time Major winner/and the current #2 ranked tennis player in the world, so it's unheard of for players of that caliber to have such a huge disparity for 10+ years. Even Borg didn't beat Connors for more than a couple of years without a loss, ditto Chris versus Martina N. when they were overmatched.
Serena doesn't have that kind of lopsided record with her other major competitors, namely Venus, Jenifer Capriati, Martina Hingis, Kim Clijsters, Lindsay Davenport, Justine Henin and even recent players like Viktoria Azarenka, who has beaten Serena 3 times in the last 5-6 years.