I am talking about Laver growing up in modern era with modern tech. In the modern game his physical limitations would soon become apparent. It's not even about talent, it's his lack of height, athleticism and brute physicality that's required today. He would probably be on Ferrer's level, but nowhere near a slam.
Not necessarily true. Laver was 5-9 or 10, Rosewall 5-7. Had they been born 40 or more years later, chances are due to nutrition and evolution they would be a few inches taller, and therefore, stronger. Still, despite their size they were beating players taller then they were. Gonzalez was 6-2, Newcombe, Hoad, Emerson, Roche, Ashe, Passerall were 6 footers or close. With modern equipment and training techniques, great athletes of the past would be great tennis players today. The same is true of any other sport too.