Sandy Leon's offense:
Since the beginning of July, his line is .129/.201/.197/.398 .
Since the beginning of August, his line is .101/.184./.188/.373 .
Leon is in such a horrendous slump offensively, that he will almost have to be pinch hit for in a key situation in the playoffs. And that key situation might come fairly early in the game, like the 4th inning.
Because of that, I really don't think it's a bad idea to have both Vaz and Swihart on the roster. I understand that Vaz won't offer much in terms of versatility, but it will give Cora the freedom to pinch hit for Leon at any point in the game, without the concern of losing the catcher. Swihart offers that versatility, including being a pretty good runner.