I think the argument is valid. Much of the value of attending a live sporting event or concert is that nobody involved knows how it's going to turn out. You get to experience an unfolding spectacle in real time.

That's not what a world's fair is. A modern world's fair would be essentially a bunch of companies showing off their latest inventions, in a highly coordinated and controlled way, for marketing purposes.

A better analogy would be something like E3, a video game convention which is struggling to find its purpose in a world where it's easier and more effective from a marketing standpoint to just release a video of your new game. I think it's no coincidence that world's fairs stopped being as important right around the time mass communication became ubiquitous.