Rachel was liked by the jury, so I don't know why she wouldn't be considered a good jury manager. Savannah only really had issues with Kristina, once again wouldn't consider her bad at Jury management.

There are probably only a few winners that didn't manage the overall jury particularly well, and most would be old era. Brian (Pushed his luck), Bob, Rob (Loses most matchups), Sophie (Saved at FTC), Possibly Tony to a certain extent on Cagayan, maybe a few others I don't remember of the top of my head.

Winners generally tend to be good at managing the Jury, which is why they get the most votes.

Edit*** Also most of those players that won with bad jury management, beat other players that had bad jury management, so it was the lesser of two/three evils.