You are presupposing that any of Keanu Reeves’s films can stand on their on now (a big presupposition on your part). My dislike of him knows no limits, and if anyone remembers him 70 years from now I’ll eat your hat.
Gilbert and Reid are extremely poor examples of what you’re talking about (and, of course, the word isn’t “ingenue”). Both were silent film actors who never really made a transition to sound – Reid because he was dead of a drug overdose, Gilbert because his florid dialog from the silent days sounded silly on screen (along with supposed problems with how his voice sounded). Once sound came in, silent films got short shrift.
As far as future reputation is concerned, neither will be forgotten. Reeves especially has made too many good films(e.g., “I Love You to Death,” “My Own Private Idaho,” “Tune in Tomorrow,” “Feeling Minnesota,” “Speed,” “A Walk in the Clouds,” “Much Ado about Nothing,” and “Little Buddha”). He’ll probably be remembered as the star of a bunch of well-made but quirky small films.
I don’t know why people hate Reeve’s so much. I mean, he’s not necessarily “bright” as far as factual information goes… but he has talents too. Just because he may not be strong in the same areas as other people, doesn’t mean he’s not on the same level. People say he’s a bad actor… I think there are some roles that are perfect for him. Maybe I just root for the under dog. Did the same to Jim Carrey… I didn’t even like his films but I liked him and his story… now look where he is now. Doing drama and being praised for it. People were skeptical. BTW, who cares if he’s remembered, there are many degrees of success.
Directors Cruise has worked with: Kubrick, Spielberg, Scorsese, Coppola, Stone (and to lesser degrees Levinson, Crowe, PT Anderson, Pollack, Reiner, Howard, DePalma and both Scotts)
Directors Reeves has worked with: Coppola, Bertolucci, Van Sant, Frears, Raimi (and to a lesser degree Howard, Bigelow, Kasdan, Branagh & the Wachowskis)
Not all of these films are great by any means, but both actors (particularly Cruise) have made efforts to work with a wide variety of talented people, often in a variety of different or innovative roles.
Clark Gable wasn’t that great of an actor (he rarely makes the list of the “great” screen thespians), but he definitely had a particular cinematic charisma; he was undeniably a star: people remember him for the force of his personality and his association with large, successful projects. Cruise will do the same (or probably more, given the trajectory of his career currently).
Reeves is harder to nail, but his career is peculiar enough that it can’t be considered merely accidental that he’s associated with so many good projects (though he’s rarely the best thing about them). Still, the movies will be remembered (which was the OP’s question) regardless of how often his career is evaluated and re-evaluated.