This was a mistake, right? It was clearly meant to be Cena (so he could lose against Cody and turn heel after Mania). If you watch the moment back Jey sits in the ring repeatedly muttering to him "oh shit" cos he realises how badly he just fucked up.
Jey Uso will always be midcard tag team, no matter how hard they try to make him 'main event'. The whole reason he has that moniker is because it's basically a joke - actual main event stars don't need a name like that.
He had the worst Mania match in years against Jimmy, and has no in-ring character beyond "like Roman, but worse".
I refuse to believe they intentionally had him win the Rumble, there's just no fucking way they're that stupid.