The further this show moves away from its source material (the Stephen King novel), the more it must attempt to answer its own questions, but Rebecca's plan to assassinate Stillson still feels like a rehash of "Zion" since it is, after all, just another reworked version of the novel's ending (of course, her motive is far more personal than Johnny's, but just as effective).
I like the Greg Stillson that the show has given us; I like that it was James Stillson, and not Greg, who took Rachel Caldwell's life, and that Greg retaliated as he did. I can identify with this Greg Stillson far more deeply than I can with the ice-blooded single-minded embodiment of evil that the novel and film presented; the Greg Stillson of this show is, dare I say it...more human?
Of course, in this attempt to humanize Greg Stillson and make him a more believable character, the show's writers have forced themselves to reintroduce the villainous menace that Martin Sheen so aptly portrayed in the film. Enter Malcolm Janus, the frontman for a black-bag Illuminati-like organization that plays chess with politicians and preachers alike; Stillson thus becomes a puppet to a global conspiracy, and the mythology goes on.
Johnny throwing away his cane serves the writers more than it serves the story. Considering the magnitude of the future that Johnny is trying to overcome -- nuclear disaster and human apocalypse -- one should think he'd want access to every piece of information he could get; add to that the unique perspective of having a personal pipeline to the other side of said disaster, and Johnny now has the potential to attack the problem from both ends -- before AND after it happens.
Clearly, Michaels Perry and Taylor wrote Johnny to throw away his cane in order to unsaddle the cumbersome plot that Future-Johnny was becoming. That Johnny's own future-self would manipulate him, and for what reasons, raises some interesting, and subsequent difficult, questions that the writing team might not have wanted to deal with. I tend to believe (based on the "Believe" graffiti that Johnny saw in his post-Armageddon visions in "Finding Rachel, Part 1") that Johnny has some kind of devoted cult following in the future (he did, after all, correctly predict Armageddon, did he not?) that has elevated him to the stature of prophet-deity, and he wants to hang on to that power.
Fortunately for the story, Johnny threw his cane into a rive in Washington D.C., where Christopher Wey is said to have found it in 2015 in "Visions," so the Armageddon timeline remains intact.