We don't know how long Kuma's been part of the revolutionaries, but we know he's been there since Luffy was 8.How long has Bartholomew Kuma been part of the Revolutionaries?
Did he join during his time as Shichibukai or already before?
I tought it was the latter. But then I don’t quite understand why at the end of Thriller Bark he let Zoro go through such a pain?
Or do you think he made it in order to test Zoro ? To make him stronger?
Did he not use his full powers on Zoro?
(That is the only explanation I can think of.)
Kuma wasn't supposed to kill the Strawhats, but to make a show out of it he decided to knock them all out an inch unto their lives. Zoro just made it complicated and thought that by taking on all of Luffy's pain he was doing the right thing. It would have been better if he stayed down logically, but then we wouldn't have that epic ending.
No, he didn't use his full powers on Zoro.