I don't think it's possible to call one single athlete as the ultimate GOAT of any sport... even in more objective sports like football people argue all the time about who's the greatest (Maradona, Pele, Messi or Cristiano Ronaldo?) and it's probably even more complex in a sport like figure skating, where the rules, technical difficulty, judging and other elements are constantly evolving.
It would probably be easier to agree on who's the GOAT of each particular era of figure skating. I haven't been following this sport for long enough to have an opinion on Michelle Kwan, Katarina Witt or anyone else from the old days, but for me, Yuna Kim is the greatest of her era and Alina is already the greatest of hers.
I agree that maybe Alina's career is still short to compare it to the careers of other greats, but in only 2 seasons she has already made sure her name will be remembered in the history of figure skating. Her Grand Slam is no small feat and I'm sure we won't see anyone else repeating it in a long time.
As she is only 17 and still competing, her legacy is still being written too and I'm excited to watch her career unfold and see her evolve as a skater
PS: This argument never ends, because who we think is the "better skater" also depends a lot on our personal taste. I prefer the "Russian style" of skating and particularly Eteri's school... I can also appreciate the slower, lyrical, more princessy styles but they're usually not my favorite programs or skaters. I have noticed that a lot of north american fans seem to prefer these types of programs and I think maybe that's a reason they don't like Alina's programs.