For me, the arguments against Navratilova as GOAT are as follows:
1) At 18 majors versus 22 for Graf, why does it suddenly become relevant that Navratilova has so many more doubles titles? Martina didn't win those doubles titles alone and she surely did not have the same level of competition as a doubles player that she had as a singles player. So, why does that matter and just for her? On the men's side, how ridiculous would it be to claim that John McEnroe is greater than Sampras or Federer based on his number of doubles titles?
2) Of all the contenders for the GOAT title, Martina is probably the least versatile. Half of her 18 majors were won at Wimbledon. Only two of the 18 were won on clay.
3) At Martina's peak, she did not have the best competition of the four contenders for the GOAT title. She probably had the worst.
4) Of all the contenders for the GOAT title, Martina is probably the only one who actually campaigned for the title, both on the court and in press conferences. So, maybe we should judge her by her own high standards.
At her peak, Martina set out to win a calendar year, grand slam to match Margaret Court, but came up short. With Chris at least, we can say that the grand slam didn't mean as much as it did for Margaret, particularly in view of how the majors were somewhat diminished at Chris's peak by the emergence of the WTA tour. But, you can't say that about Martina. She knew what it was and actively sought to complete one. So, what does it say for Martina that an 18 year-old, one year removed from winning her first major, sweeps the majors, including Wimbledon by beating Martina no less.
It is almost like the Gods on Mount Olympus were trying to tell Martina something. You're not the GOAT, Steffi is.