Actually, there are more layers of deniability than that.

Lazarus Long may have said that, but he may or may not have believed it. He was encouraged to just talk, and he very clearly wasn't putting together a codified system of what he believed. Also, he was known to lie.

And we don't have a full transcript of what he was supposed to have said-- it was a computer-edited compendium of advice, and the computer may have had her own agenda.

Did Heinlein believe everything in the Notebooks of Lazarus Long was good advice? Or was some of it just characterization?

Getting back to the book, LL had longer to acquire skills than ordinary humans.

And, for a counter-argument, see Brin's Glory Season-- one of the reasons women are in charge is that men think they ought to be good at everything and don't get the advantages of specialization.