The FBI used to at least appear to have shrugged off Hoover's corruption, and the human trafficking cases/kidnappings they've broken open over the years do give the field level agents some cred to keep with the public.
I actually have a theory on that.
Hoover, for all his corruptions, was arguably a right winger. He hated commies and leftist infiltration, and generally pushed against what he thought was "degenerates". Thus when he politicized the FBI, he politicized it in a right wing manner. Thus as his influence was purged, the FBI did, indeed become a politically neutral organization from shortly after his retirement until the Clinton Administration. The Clinton Administration is the administration that really started the modern era of politicized bureaucracy (and it became their main way of getting things done after they lost the House and Senate in 92), though they mainly impacted higher levels, not rank and file, as they had a very hostile House that was keeping an eye on them. But the entire "right wing militia" being a threat all started under the Clinton administration and it was Clinton administration stuff where you see things like Ruby Ridge and the like.
W. of course put a pause on politicizing the bureaucracy, but he also greatly empowered the security bureaucracy in a way that no other President had due to the War on Terror. Obama, however, is where the politicization really ramped up. While "ideological tests" for employment in the Federal government is actually prohibited by law, the Obama administration instead utilized other tests that when used together would 90% of the time result in solid progressives being hired; things like looking at where people were from, what school did they graduate from, ethnicity, religion, etc., and favoring the combinations which resulted in the hiring of progressive activist types, thus systematically politicizing the bureaucracy.
So, combine the early politicization and obsession with "right wing militias" under Clinton and then the systematic politicized hiring practices of Obama, and you get an FBI that went from corrupted by right wing influences... to corrupted by left wing influences, with a brief window where it was non-partisan that enough people remember that they are blind to its modern corruption.