Another reason a plea deal is an aweful outcome is because there's nothing stopping some other nation-state trying to prosecuting Assange, and keeping him jailed forever. There are 194 other nation-states on the planet, and who knows how many of those have extradition treaties with the UK; any one of those could seek extradition of Assange for whatever BS. The US Federal government could easily use any one of those as a pawn to keep Assange in prison forever.

If Assange takes the plea deal, the US Federal government can still murder him after his release.

Assange is in a no-win scenario, and the criminals responsible get treated as heroes by their fellow countrymen.