But it's been reported there's "no market" for Joseph. There are not many teams looking for a shortstop. Rupp's not attractive. Even though they offer controllability, they aren't clear upgrades for contending teams. So sure, if you could get good deals for them, avoiding some roster decisions in November would be part of the appeal. But not a reason to make a bad deal.
If the choice is between losing Joseph for nothing and losing Pullin for nothing, it's not a simple choice. If the choice is trading Joseph for two decent prospects vs. trading him for one decent prospect, the net loss is one player regardless of whether it's the trade return or a Rule V exposure. If the Phillies lose two players in the Rule V but then manage to swap Hernandez for a starting pitcher, I'll take it.
And most returned Rule V guys get returned in spring training or very early in the season.