As far as dominance in the majors, I'd easily take:
Court, and her 1970 Grand Slam year, plus 1963, 1965, 1969, and 1973 seasons (and even if you only count Open era, Court's dominance in the majors outranks Seles').
Navratilova's 1983-1984, plus 1985-1987 seasons
Serena's 2002-2003, 2010 seasons.
Chris Evert's 1974-1975-1976, 1980 seasons
Connolly's 1952-1953 seasons
OVER Seles' 1991-1992 seasons, when looking at it from a dominance perspective. And in this case, less is not more, in terms of # of dominating seasons. I mean if you have 3 dominating years in the majors, doesn't that outrank two, or one!
I will repeat myself.
In Elo method, dominance duration does NOT count. Only dominance level. Of course Court dominated 5 years, Navratilova also five. Also great was Evert, not mentioning Lenglen and Wills, that you forgot.
All these players could have dominated 20 years or more, there's no difference.
you are only looking at dominance level, it's easy to notice that between 1991 and 1993 Seles played 8 majors, won 7, only losing one match to Graf (who is - without any doubt - one of the most likey GOAT candidates). She defeated Graf (twice), Sanchez-Vicario (3 times), old Navratilova (twice), Novotna (once), Sabatini (3 times).
If this is NOT supreme dominance, I don't know how to define such a thing.
Well, Navratilova 1983-1984 dominated. But she "only" won 6 majors, losing to Horvath and Sukova. Losing to a low-ranked player such as Horvath is a disaster, comparing to losign to Graf (in Elo method).
But there's Court in 1969-1971. Well, she's better than Seles, having won 8 majors, losing only to Haydon-Jones - better than Horvath, still no Graf. And Court only defeated King twice, Goolagong twice. Much, bur not as much as Seles. Plus, don't forget she only played 49 matches during 9 majors (winning 48), while Seles played 56, winning 55, despite competing in 8 events. That's why Seles is higher than Court.
Serena played 6 majors, won 5. No match.
Evert played 8, won 6. Very good, and she defeated Goolagong 3 times, Navratilova also 3 times. She only lose to Goolagong and King. That's very good, and she's very close to Seles, but still not equal.
Connolly extraordinary. 9 over 9! Her problem, she did not defeat strong players. Hart, Fry, Brough are top 30 (alltime) at best. And she played 51 matches only.
So, why is Graf ranked higher (more or less, she's equal)? Because between 1988 and 1990 she won 8 majors, played 9, only lose to Sanchez-Vicario (better than Haydon-Jones), defeated Navratilova (3 times), old Evert (3 times), Sabatini (4 times), young Seles (twice), young Sanchez-Vicario (once). I think Seles defeated better opponents, but Graf won more, and more matches (62 over 63).
Now the difference between "dominance level" and "dominance duration" should be clear. Of course I know that Graf dominated more years (there are 1995 and 1996, of course), won much more than Seles, so she's a better GOAT candidate than unlucky Monica. But dominance level is the same.
Or, we can also say that "dominance level" = "strength at best" (if consistent). So, the old question, "was Seles really better than Graf or was Graf not at her best during 1991-1992?" could be settled, as the two players were of equal strength (according to Elo).