why is john walker getting so much hate? the character is flawed but he's got a big shadow cast over him by steve rogers and he's nowhere close to him, his frustrations are very understandable imo.

you can only do this move on vampires, though. And specifically Nazi vampires!

I don't think Sharon is the PB, it doesn't fit the way she ran into Sam and Bucky after the assassination of that other crimelord or whatever. I'd also be annoyed if it turned out she chooses to stay as the PB after being offered a full pardon (if that happens - ep 5 was all talk and I kept hoping Sam would mention this was somewhere in the pipes, didn't happen)
Sharon was the one "big" SHIELD agent who didn't join Hydra, I'd be really annoyed if she ended up as the PB creating a Russian super soldier serum just because she can't go home.

USAgent ending up with the Thunderbolts was a day one prediction, but now that Madam Hydra is the one approaching him, it feels like Ross will start as a self-righteous general who isn't outright with Hydra, maybe Veep is still pretending to be SHIELD, but once she reveals her title, I feel like Ross will be the kind of general who doesn't give a shit as long as it works out for his objective, and he'll end up siding with Hydra. The only problem is that making the Thunderbolts a subset of Hydra would be a bit of a letdown for them, they'd have to give them a storyline to go to and not just be Hydra's new strike force. Maybe it could swerve toward AIM instead, I don't know if Yelena would join Hydra (if she joins the Thunderbolts instead of just becoming the new Black Widow for the Avengers), but Abomination and USAgent would be a good match for AIM. Ghost... Maybe as long as she gets to live.

As for the PB, it could be Ross but only because it's the only big name we've seen so far that's remotely associated with the whole affair, and even that is only because we expect the Thunderbolts to make a move on Johnny-no-vibranium. If it ends up being him, I feel like it'll be only because Veep manipulated him into taking that role. They simply gave zero information on that figure, everything is circumstantial because this person happened to be standing there at that time, so anyone can be a red herring, starting with Sharon.
The PB could be a random nobody and it wouldn't change a thing to the story so far, so it feels like it's only intended to prepare the terrain for something else in the future. I don't see why someone like Ross who wants to make his own Suicide Squad would be the PB of the underworld just like that, if it's him then it has to be some manipulation for something like Hydra, and Ross just doesn't care.

Oh yeah, the only thing we know about the PB is their work with the super soldier serum, that's how Ross could be connected, but I think the doctor said he started his research from Russian versions, right ? Ross is still working from Banner's version and the original tests after Cap / Weapon 1. Hydra would be closer to that, and if they're gone, then AIM is the remaining entity that could have picked up the pieces of Hydra's work.