I think Wrestling, because it is an art form in the end, what you determine to be valuable will determine who you think is the best. Like sure, you can look at "Who draws the most money" then point to Hulk the Racist, Cena or Austin, even Roman now. In ring wise, you like, you may point to Flair, Rey Mysterio, Vader, or Danielson, depending on what you like. Then there's the mic work, and moments. Maybe you think Rock's the Goat for his smack talk, or you are attached to wrestlers who gave you amazing moments that made you feel.
So the GOAT will be up to debate. But calling Danielson one of the best of all time, I think on multiple factors you can make that argument and I'd support it.