I've read a little Clarke and one of Asimov's (I may have read one Heinlein short), so I may not be well qualified...
But those were the names that built the genre my father still loves. These were forward-thinkers, exploring ideas about things that may come - and, in truth, have come. And even a lifelong fan like Dad, looking back on them, can see that the stories themselves are somewhat dated, even if the ideas and concepts have withstood the test of time. (Actually, I think Asimov himself acknowledged this effect. IIRC, in one of the sci-fi anthologies he compiled of old 1930's-ish sci-fi tales, Asimov comments that it wasn't until he was going back over the stories to compile them that he realized how ridiculously racist the old sci-fi stuff was: all black aliens were brutish and evil, all yellow aliens were devious and clever, all white aliens were good, etc. But at the time he first read them, he didn't even see that; he just saw the ideas and such that inspired him. Because he was as much a part of that era as the writers were. Even as an iconic sci-fi author, a man who should, theoretically, be able to envision the future and craft Ideas beyond prejudice and the distorting lenses of his own era, Asimov had his blind spots. As do we all.)
I suppose my equivalent would be Tolkien, in fantasy. Were his books groundbreaking? Yes. Did they leave an indelible mark on the genre? Clearly. Can they still be enjoyed today? Quite obviously. But are they somehow sacrosanct, incapable of aging or impossible to critique because of Who Wrote Them, a Grand Master and Father of Literature? No book is beyond that.
(I guess I just don't like the idea of cordoning off certain works or authors, setting them on pedestals to be worshipped. One can acknowledge the import and impact of a book, or a person, without transforming them into a larger-than-life icon beyond question, as sometimes seems to happen when people label things as The Greats.)