As we've seen in seasons past, the best vocalist does not neccessarily win the prize. Prime evidence is last season when Pia was eliminated. She couldn't be saved since the judges wasted their one save on Casey (who wasn't going to win it anyway). But she was clearly the best voice of that season. At least this season they held their ground and didn't waste their save on someone like Deandre (as JLo wanted). And regardless of whether or not she wins, she'll have a successful music career.
Of the contestants remaining, I think she and Skylar will be the mosts successful. Others will do okay and carry a niche audience, but either of these two will be singing to large sold-out concert halls. Jessica has the better voice, by far. But Skylar has a great voice, but also knows how to work the audience and get them into her performances.
The truth is incontovertible. Malice may attack it and ignorance may deride it, but in the end, there it is.