It was deliberately conspicuous that MIB gave Ricardo instructions on how to kill Jacob that mirrored Dogen's instructions to Sayid on how to kill MIB.
But nota bene that Ben did not get the same instructions before actually killing Jacob. Specifically, Ben heard Jacob talk, and killed him anyways, whereas both Sayid and Ricardo are told that if they let their target speak, it'll be too late.
I think this supports seeing Ben as exceptionally free-willed, outside the direct control of either side. He may well have a Gollum-like role to play in the final denouement. He's the only character we've seen who was ever under MIB's sway and then came back to the other side-- this could set up a Gollum-like re-fall from grace (with unpredictable consequences). But my guess is rather that Ben's real proof of the ability to go on choosing.
Ben chose darkness a long time ago, in arranging for the Purge. He lied to the Others for years, claiming to speak for Jacob but never actually meeting the guy. He visited the cabin in the woods that was probably holding MIB prisoner, but on his own telling he never saw anyone in it, so he never spoke with MIB either. (We don't yet know whether Richard knew Ben was lying and let him get away with it, or for some reason was kept in the dark.)
Ben's spent decades nursing nasty grudges-- killing dozens to get even with his father, overthrowing Widmore and starting a bitter long-term war on that front. He resented Locke for being chosen leader and for getting to talk with Jacob. And he killed Locke out of petty envy-- then was easily manipulated by Flocke into killing Jacob with petty resentments. We'll find out that much of the Survivors-Others conflict of the first few seasons was just what it first appeared to be: Ben's own nastiness, with Jacob just serving as a religious pretext.
But after all that, even Ben could repent-- on his own, with neither Jacob nor any of Jacob's representatives leading him there.