This is not true at all. For instance Nepominatchi commented on game saying Niemann's play was "more than impressive"[1]. Not commenting on the situation per se, merely your "clear consensus among other top chess players" comment.
That's the majority of the players in the Sinquefield cup. Even Levon, who was initially skeptical, has since reversed his position.
As is tradition in chess, no one says "He cheated" they say things like "his moves were better than one would have expected" or "superhuman" or "I felt like I should trust my opponent over my calculation".