The same WP article on Venus in fiction referenced by the OP documents one specific scientist who believed, in a nonfiction sense, that Venus is indeed the world envisioned by mid-20th-Century writers:
In 1918, chemist and Nobel Prize winner Svante Arrhenius, deciding that Venus's cloud cover was necessarily water, decreed in The Destinies of the Stars that "A very great part of the surface of Venus is no doubt covered with swamps" and compared Venus' humidity to the tropical rain forests of the Congo. Because of what he assumed was constantly uniform climatic conditions all over the planet, the life of Venus lived under very stable conditions and did not have to adapt to changing environments like life on Earth. As a result of this lack of selection pressure, it would be covered in prehistoric swamps.
So it might have been, actually, billions of years ago before the greenhouse effect went bad, but that is beyond the current scope.
The 1950s version of War of the Worlds had a slight problem with this belief. The Martians, faced with their planet nearing exhaustion, needed to find a new home, and Earth was supposed to be their only alternative after studying all the planets. Having Venus as another habitable planet would have ruined the plot. So the narrator skipped that planet because the Martians, suspiciously like the Earthlings before the Venera space program, could not "see and study" Venus under its clouds. Today the narrator might say, "They seriously considered the beautiful planet Venus, only to learn that the world was livable only within the clouds. They could not build floating cities, so they could not go there."