Curious in reading Lundwall and Lewis, it is the post-Campbellian magazines of Fantasy & Science Fiction and Galaxy that appealed to European critics more than the drab technical work of Gernsback and Campbell.
I have previously noted that the Campbelline Revolution never thrives where and when Campbell is not present, and that attempts to graft cuttings from the Campbelline tree onto French and Japanese science fiction inevitably wilted.
Further, with the pulps, that the pulps died because editors like Babette Rosmund thought them passe and tried to correct the tastes of their writers and readers. The result: the readership left years before Street & Smith killed their pulp lines.
"When the Vernian monopoly of American science fiction--and through that, of a large part of post-war science fiction from other countries--finally ended (thanks to such editors and authors as Ilya Varshavskiy, Robert Sheckley and Donald A. Wollheim)"--Lundwall (h/t JD Cowan)
Read that as "When Campbell's influence ended." As Malzberg said in Breakfast in the Ruins, Campbell's influence ended because he listened to fans tired of depressing stories and put his foot down. Galaxy and F&SF gave writers an outlet for all the depressing stories writers could write.
Let's be honest, until 2010, it was editors who defined trends in science fiction, not the readers. Part of the upheaval in the 2010s is that there is now more than just an escape valve from the Nielsen-Haydens' vision of science fiction.
This, and science fiction as scripture, are the reasons why the genre has to eternally relearn Ellison's complaint: "Before you can educate, you first must entertain."
It is ironic that an entire generation of editors who blindly copied Ellison never managed to learn this lesson from their hero.