Borg and Pistol are just about the two most unassuming studs you're likely to find, while Rod is a strict follower of the old Aussie way. OTOH Budge reportedly boasted (at least in private) that Sampras would do well to get a set off his younger self while touting Pete as the next guy to win the GS, Gonzales was hardly shy about his place among ATGs (Hoad was the only one he could envision himself losing to), and even now you can read Mac between the lines and hear him thinking he'd more than hold his own against the Big 3. And can you imagine how much self-promotion Jimbo would be engaging in if he had as loud a megaphone and a stronger resume to back it up?
That Martina is singled out vs. those guys may require several explanations, but one of 'em clearly makes the most sense. All the more reason why she should keep being obnoxious!
An unintentional omission on my part. I firmly place Graf among the GOAT pantheon, though the Seles stabbing is perhaps the one valid asterisk in tennis history.