Like everyone else, I'm a mixed bag - in other threads I have addressed the parts I've liked and I've even defended the parts I didn't like or suggested ways in which what we have been presented with might work (the midair conversation in front of a jet engine at the end of the Court of Owls, for example).
Jason's Robin suit is actually one of the suits he used, comparing that with an enhanced replica doesn't work in the same way. Preserving the original card would, however.The card could be blown up and hung in the cave for the same reason Bruce keeps Jason's Robin suit - to remind him of a failure. Keep him on edge. If Joker's going to be a part of his life, he's going to be completely aware of it at all times.
He could - much as he tried to do so with Lincoln March's revelations in CoO - but too much salt isn't good for you...As for how Joker got into the cave - I agree if that's the story they're sticking with, it's a little bit of a stretch. But even still, as I said, there could be some other swerve on how the card got there. To answer your initial question, maybe it ISN'T it. There's still a bit more of the story to come. Though only one issue, if he feels like it, I feel Snyder could still tie things up nicely.
I'll wait and see.