Again, it's weird, because Legosov isn't even the primary source for the series, which is an explicitly fictionalized recounting of what happened. As Gessen points out, your thing about Legasov being part of a team is literally a character in the series!
> because Legosov isn't even the primary source for the series
I think it was explicit that the series framed the tapes as the "revelation"; the honest message of a dying man to the world to expose what actually happened
I think you're over-reading what was really just a dramatic framing for the series. The author was explicit that he used composite characters and multiple sources.
It's not a documentary! That doesn't mean you can't criticize it (Gessen sure did). It's that a lot of the kinds of criticisms you make don't make sense given what the show is.