Are you familiar with Phillip K. Dick's letter to the FBI (1974) accusing Lem of being a Communist committee that had infiltrated the Science Fiction Writers of America? Because he was too brilliant, too widely educated and wrote in too many different styles to really be a single person. Yup.

As for Heinlein -- I, too, read and loved Stranger in a Strange Land as a teenager. But even at that age I was weirded out by his habit of making sluts of all his leading ladies, and having them make babies with their fathers, or father figures (read: Heinlein stand-ins). This shit is just gross, my dude. And the older he got, the hornier his female characters became.

Asimov, Bradbury, Michael Moorcock, JG Ballard. Le Guin. There are dozens of writers whose place in the cannon is ahead of those two.

That's my opinion and you are welcome to yours.