AFAIK it is a well-known estimation, and 'fringe' may be considered weird given its main author's pedigree: https://en.wikipedia.org/wiki/Chernobyl:_Consequences_of_the...
It may. I don’t think that’s the consensus view though and again something being well-known doesn’t make it the consensus.
I’m not saying that WHO’s and IAEA‘s figures are perfect and flawless but they aren’t widely challenged either.