he has never once published anything that puts Russia or US Republicans in bad light

I don't think that is true. With regard to Russia: https://wikileaks.org/spyfiles/russia/. Wikileaks started publishing stuff about the US during the Bush presidency, and continued into Trump. I think the main factor would have been what was available to them, in terms of leaks not already exposed elsewhere. Certainly the evidence suggests they published leaks provided them to by what is likely a state (Russian) sponsored group, and that formed part of a broader pattern by that state in interfering in the US's elections, but that is not to say they wouldn't have published unreleased leaks in the same circumstances if they had them about another political party.

a country that doesn’t extradite to the US (Sweden) to a country that does (UK)

Sweden has an extradition treaty with the US: https://www.state.gov/wp-content/uploads/2019/02/10-201.22-Sweden-EU-Extradition-Treaty.pdf

There has certainly been a smear campaign (psyop?) against Assange to mislead people into hating him - and reading things like your comment I think it may have been quite successful, at least with Americans.