I can think ot two classical SF writers that can compete with the great Anglo-Saxons writers (Huxley, Orwell, Bradbury, Heinlein…) : Jules Verne and René Barjavel. They have both that strong vision and didactic style ; even if Verne is mostly SF by accident.
After that, we have some great storytellers, but no great writers like what can be found in Sci-Fi New Wave (Ballard, Disch, Dick, Brunner, Spinrad…)
I think the main difference would come from the nature of the writings ; a lot of French works are questioning the society and its evolutions (beginning far earlier than the American New Wave), while the American one is a lot more optimistic (apart from Cyberpunk subgenre) and with a tropism for space (and beyond !).
I don’t want to dismiss all the French SF litterature ; it’s only that, when in the Noir/Detective stories/criminal novels genre, we have great writers that can play on world level, Sci-Fi French writers don’t bring much to the table.
Of course, in cinema and comics books, the sci-fi creation is far more interesting and can be compared for its richness of themes and interogations to its US counterparts.