What he was trying to do was rate comics as to their importance to the medium, not value.
By that criteria there is some basis to make the claim that Detective 38 had more influence over the comics that came after it then Detective 27 did. Whether there was a Batman or not, there would definitely be more superheroes. But if not for the success of Robin we probably would not have seen nearly as many sidekicks. Does that argument hold water? Maybe, maybe not. But it certainly shows me that DC did everything in its power to hold Marvel back...without Robin there would be no Toro!
I'd argue that without Robin, Batman may have been a second-tier character who didn't survive the Golden Age. Robin gave readers someone to identify with and gave Batman someone to interact with. Batman as a solitary avenger is a limited concept. Superman had Lois Lane, Doc Savage had his aides, etc.
That said, the bronze to present interpretation of Alfred makes Robin superfluous as a character as he perform same or similar story functions but is a better character overall.