He didn't need to "manipulate" the Obama administration. Whatever he said became the policy absent any pushback from someone else. And what became US policy likely became EU policy since the US was in the driver's seat. I'm not saying the EU loved Shokin. I'm saying that they probably didn't initiate any demands that he be removed.

As for whether or not Biden fired Shokin to help his son - well, that is what the investigation was for. The one that didn't happen. We can be sure that whatever Burisma wanted from Hunter, it got - or it wouldn't have kept him on the board until Zelensky came in and continued to pay him outrageous amounts of money to do nothing.

The reason that's in Ukraine and not Brussels or the US is because it's likely in any investigative materials on Burisma that might be in the MVD of Ukraine or the prosecutor's office. Burisma almost certainly destroyed whatever files were in their possession, and I doubt the Bidens would be stupid enough to engage in a bribery scheme that left a giant paper trail in the US (though stranger things have happened).

As for why it wasn't a scandal then - both parties were pretty united in their unqualified and blind support for Ukraine. I remember it. Russia may be authoritarian and bad, but Ukraine isn't really much, if at all, better. We waded right into a deep-running conflict without thinking through the consequences, and both parties were cheering it on at the time. Joe Biden could have shot someone on Kreshchatik in Kiev and no one would care, to paraphrase a famous quote.

I can only speculate about what Burisma is getting from Kwasniewski, but if I had to speculate it's because he's been leading the EU Parliament's coordination with Ukraine and so is able to set, or at least heavily influence, EU policy with respect to Ukraine. I realize the Parliament doesn't actually set the policy but I suspect that its conclusions are the basis of the policy. Likewise, I can only speculate regarding Cofer Black, but the likely answer is that no one is ever "former" CIA.

Finally, I was only making a general point about the power of the US. If you concede that the US can but believe it didn't want to, it's possible that at the time it didn't care.