I've now gone through two well-known pieces of critical analysis of Heinlein's work, and found that they broadly (and in places exactly) agree with my initial sentiment. Far from "feminist twitter", they are written by serious science fiction critics during Heinlein's lifetime. Below are some quoations and references. I have yet to find compelling evidence to the contrary in my research.
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> Heinlein's male characters may be divided into two categories: the competent and the incompetent. The incompetents are of little use in the practical world. They function mainly as caricatures for purposes of contrast, satire, and humor, and include such types as the spoiled brat, the jellyfish father, the pompous blowhard, and the bungling meddler. The competent male characters are divided into two types: the stock competent and the Heinlein hero.
> There are a goodly share of failures due to Heinlein's discomfort, and his subsequent exclusion of emotions and arm's-length distancing of the intimate.
> The Heinlein heroine ... stands as a—pardon the expression—male chauvinist tribute to the hero, implying that women—even such as the heroine—enjoy being dominated. ... Heinlein himself could not break away from his own emotional attachment to the obedient female.
Ronald Sarti. “Variations on a Theme: Human Sexuality in the Work of Robert A. Heinlein.” (1978)
https://www.enotes.com/topics/robert-heinlein-61736/criticis...
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> The Moon Is a Harsh Mistress is totally a story of process rather than character. Heinlein has always been more interested in how machines and societies work than in why people act, and this is probably more true of this novel than any of his others. And it is the center of what is wrong with it as a story ... Heinlein has always had a weakness for forcing emotion, possibly because his characters themselves are unemotional. When Heinlein wants us to approve a character or a position, or to feel moved, instead of giving us a natural emotional reason growing out of the story or, alternatively, underplaying, he is all too likely to try to find a button in us to push.
> Heinlein's concern with his religion [in Stranger In A Strange Land] is so great, unfortunately, that he lets all character development go hang. Mike Smith is lessened by his super powers. ... Jubal Harshaw, too, is lessened by his super powers -- doctor, lawyer, etc.; his multiple training seems a gratuitous gift from Heinlein without reason or explanation. He redeems himself somewhat by his crusty nature, but I find him suspect. He is too pat. Some of the minor characters have life at the beginning of the story and then lose it, overcome by the flood of talk that engulfs the last half of the novel. Which secretary sleeps with Mike his first time out? They are so lacking in definition that it is impossible to tell. Jill Boardman supposedly loves Ben Caxton, but won't sleep with him. She will, however, go off around the country with Mike on a sleep-in basis. Why? I can't say. At any time it would not surprise me for her to unscrew her foot and stick it in her ear -- she is capable of anything. Ben Caxton's motivations are equally unclear.
> Basically, Heinlein has used the same general characters in story after story, and has kept these characters limited ones. ... There is one unique and vivid human Heinlein character, but he is a composite of Joe-Jim Gregory, Harriman, Waldo, Lazarus Long, Mr. Kiku and many others, rather than any one individual. I call the composite the Heinlein Individual. ... Outside of this Heinlein Individual, there is usually a small supporting cast of side men in any one book. Their most striking feature is their competence, reflecting that of the Heinlein Individual. Beyond that, however, hardly any attempt is made to individualize them, for, after all, they are no more than supporting characters, and if lead characters are not described, what can be expected for less important players? After this small circle, Heinlein ordinarily relies on caricature, and he has a number of set pieces which he produces as needed.
Alexei Panshin. "Heinlein In Dimension" (1968)
https://www.panshin.com/critics/Dimension/hdcontents.html#Co...