That McMillan should be so shocked by the idea of a story-free movie suggests he's never seen a single experimental film. (Where's the "real connective tissue" in Stan Brakhage's Mothlight?) Even if we're limiting the discussion of film history to popular narrative cinema, there are countless precedents of Hollywood spectacles that recycle familiar plots. The great Fred Astaire-Ginger Rogers musicals tell pretty much the same story every time. Chuck Jones and all the major Looney Tunes directors repeated gags from one cartoon to another (and, come to think of it, none of those are very plausible either), as did Charlie Chaplin in the hundreds of shorts he made early in his career.
The central flaws of McMillan's argument are that he equates implausibility with bad storytelling and confuses genre tropes with cliches. As Jacques Rivette illustrates in his masterpiece Celine and Julie Go Boating (screening this week at the Gene Siskel Film Center in a new print), one of the great satisfactions of film spectatorship is in latching on to familiar elements and recombining them in your imagination. Jonathan Rosenbaum, in his Reader capsule review of that movie, calls this the "wholesale ransacking of the cinema of pleasure," and I'd argue this act of theft is easier to commit where the bounty is cheap and abundant—that is to say, in the realm of genre-bound spectacle.
It's worth noting that Celine and Julie gain autonomy within the Victorian melodrama they magically enter as they become more familiar with it. Knowing how the story unfolds allows them to intervene within it and have more fun. Imagine what the two of them could pull off if they snuck into The Bourne Legacy!