Excellence, about the suitpieces. If you shield a suitpiece, we'll get to it before you, end of story. Just because it's not in the immediate grab range does not mean it's out of our reach. ZSS is one of the fastest characters in the game, she can reach anywhere pretty **** fast. Side-b does not work against suitpieces, the suitpiece will kill the pikmin and then bounce back to ZSS, meaning she'll just keep tossing until you run out of pikmin and have to pluck. You also seem to forget that ZSS glidetosses, JC tosses, and throws from the air, not just stationary throws.
Anyways, as for range, Side-B will be just outside grab range if it's tippered and not perfect shielded. I think you might be able to shield grab if you get closer to the inside and powershield it (to prevent sliding). If you make it past the sweetspot, it's easily shield grabbed.