Her peers are all tennis players, since its one sport, not two. Moreover, its greatest events and the achievement for wining (the majors) are not now, or ever considered unequal.
There is no doubt John McEnroe is suffering with male irrelevancy crisis issues; he knows male players of today & tomorrow are never going to be the super-player required to surpass Serena, so again, he--utterly frustrated (if not feeling a bit psychologically castrated) attacks Serena (and his focus is on the inability of the current top males--Nadal, Djokovic & Federer--to surpass her, as he says nothing of former great females, nor is he attempting to inflate his weakened ego issues by challenging them...telling). Worth noting again, John McEnroe cannot get out of his own way, instead, choosing to create more negative chapters for his life that--unfortunately--outnumber his achievements. With each, passing month the number of "peers" with respect for his voyages into self-interested "commentary" shrink. Fitting, considering the subject.
He cannot alter what is historical fact: Serena's record is superior to the top men of her era--and most of other eras, with the exception of the Grand Slam winners. He can cry, spin, argue or wonder why the future of men in tennis is bleak, but it will not erase Serena's superiority over his male champions who will never touch her record, or the obvious burn of Serena leaving him in the dustbin of sports history, and those who have transcended the sport.