Laver did something no one else did: he mastered the amateur tour, then the pro, then the Open Era. Rosewall did the first two, and was good in the Open Era, but he wasn't dominant, just one of the better players of the first few years, closer to Newcombe in level.
To some degree, Laver just happened to be the right age, for certain if Pancho was ten years younger, he'd have been formidable in the first few years of the Open Era, but it still holds a strong legacy element.
One angle on comparing the Big Three is isolating what each of them does better than anyone else. For Roger, it is his finesse and diverse skill set, I think. I just don't think any player has produced as many "wow" moments. This isn't a slight on Rafa or Novak, just the nature of Roger's game, that he has such a diverse tool-set to draw from. For Rafa, it is his indomitable will and competitiveness. How many times has he pushed through any obstacle, and forced victory through his fighting spirit? For Novak, it is probably his "lockdown defense,' or perhaps his ability to calibrate to the level of his competition and just play better enough to win.
All three have just about every quality of greatness in spades, but I don't think it is a slight on the other to to point out the special excellence of one of them.
I hear you about the legacy of Fedal, certainly on the level of mass appeal. It was probably the "sexiest" rivalry since Borg-McEnroe, which in my mind is still unsurpassed. But Novak's legacy has to be the fact that he's the one who took over from Fedal. I know, Rafa had dominance mixed in, even Federer a bit, and Fed fans can claim that Novak took over after Roger was past his very best. But for the last ten years, Novak has set the bar - he's been the player to beat. Rafa, Roger, Andy, and Stan have had their moments of equaling him, but it has always come back to Novak who, like the Dude (Big Lebowski), abides.
Hopefully that's changing, though! Not a slight on Novak, but I'm kind of tired of this era and ready to see the young guys take over. As you know, I think it is clearly happening, just a bit slower than hoped for.