I think Wicks is the favorite, but I do think Assad's chances are being understated by the fanbase. There's a funny thing that happens when a guy, particularly a pitcher, is lucky. Fans, even smart ones, often respond in one of two ways:
1. "Maybe he's an exception, and this is sustainable." More or less boils down to this
2. Deciding the guy is bad actually. There's a good bit of gambler's fallacy baked in here. But you'll often see "his FIP was a run higher than his ERA!" followed by a screed about how therefore he sucks. Blake Snell right now is a fantastic example of this.
But there's a third path, if the ERA is lower than the FIP by a run, ask yourself: "So how would that FIP rank?" A LOT of baseball is luck, but lucky =/= bad. Going back to Blake Snell, he pitched like an All Star last year and got luck carried him to Cy Young caliber results. But don't ignore that first part about pitching like an All Star.
Bringing this back to Assad, he pitched well, regardless of role, after he came back to MLB for good in June. His stint back in the rotation in August/September was particularly illuminating, as IMO even if you ignore the sparkling ERA he peripherally looked like a quality #4 starter.
I think Wicks' prospect pedigree and Assad's early success as a swingman is ultimately going to lead to Jordan getting that #5 spot. But if I had to win a game right now Assad would pretty easily be my choice among the four contenders and so I don't think he's too much of a long shot to grab the spot for himself.