The experts have always ranked it very high but in this case I agree with you that the level of competition wasn't as strong as even the previous year because von Cramm wasn't playing. In 1938 Budge did not have to play an Ellsworth Vines who may have been favored on some fast surfaces like grass, Nusslein who was perhaps the best clay court player in the world, his nemesis Fred Perry who would be extremely tough outdoors on grass and clay. Cochet and Tilden, while older were still very capable of defeating Budge. It would have been very tough for Budge to have a Grand Slam in 1938 against all competition. On the other end I do think it's quite possible that Laver would have won another Grand Slam or so during his peak years of 1964 to 1967 if Open Tennis was around. Laver, unlike Budge faced top competition in Rosewall, Hoad, Gonzalez, Gimeno, Trabert, Segura, Sedgman, Cooper, Anderson etc.