ASV, as mentioned, slowed down. And had wrist injury issues if I recall correctly. And had to be at least a little burnt out. Graf dropped her on her head 28 times!
I think the rivarly between Steffi and Arantxa "felt" a lot closer than the 28-8 head to head count.
After their first 19 matches (1988-1992), Steffi was up 16-3. You would think that Steffi "owned" their rivarly, but it wasn't the case at all. The 3 matches won by Arantxa were HUGE Grand Slam matches:
1) 1989 French Open final: 17 year old Arantxa beat Steffi in one of the biggest surprises in tennis history. Steffi won 7 of the 8 Grand Slam tournaments in 1988/1989, she was considered unbeatable at the time.
2) 1991 French Open semifinal: Arantxa beat Steffi 60,62. Many experts and fans consider that match the darkest moment in Steffi's career.
3) 1992 US Open quarterfinal: after slipping to number 2 in the world, Steffi won Wimbledon beating Monica 62,61. She looked ready to regain her number one ranking... until Arantxa got in her way and surprised her at the US Open.
Between 1993 and 1994, even the numbers became closer, Steffi won 8 matches (including a semifinal and a final at the Australian Open) and Arantxa won 5 (including a US Open final).
Between 1995 and 1996, Steffi won 4 Grand Slam finals against Arantxa, but they were all extremely close matches.
Even when Steffi was at her best, Arantxa was one of the few players that could drive her nuts, especially in the big matches. So you never felt that Steffi owned Arantxa.
Gabriela, like MJ, didn't seem to ever "peak".
I would disagree.
She peaked precisely between September 1990 and June 1991, when she was one match away from becoming number 1 in the world.
W US Open, def. Graf 62,76
F Zurich, lost to Graf 63,62
F Worcester, lost to Graf 76,63
F WTA Finals, def. Graf 64,64 / lost to Seles 64,57,36,64,62
Q Australian Open, lost to Sanchez 61,63
W Tokyo, def. Graf 46,64,76 / def. Navratilova 26,62,64
W Boca Raton, def. Graf 64,76
F Miami, def. Graf 06,76,61 / lost to Seles 63,75
W Hilton Head, def. Sanchez 46,64,63 / def. Meskhi 61,61
W Amelia Island, def. Sanchez 62,26,64 / def. Graf 75,76 (5th consecutive win against Steffi!)
W Rome, def. Seles 63,62 (that's when everybody started thinking GOAT Gaby owned both Steffi and Monica)
S Paris, lost to Seles 64,61
Had she won that semifinal against Monica in Paris, she would have become number 1 in the world. Gaby was 4-1 up in the first set and looked like she was going to dominate the match as in the Rome final. Then the rain came. When they resumed play two hours later, Gaby won only 1 game.