I'm really going to need an example here. I can think of a couple candidates, but there's a big difference between Reigns and Bálor in the ring: Reigns is almost completely dependent on his opponents to carry the match. What's worse is Reigns has show no real desire to improve himself in the ring. Finn Bálor, meanwhile, has not only shown a better ability to work a match, he's also shown a desire to always improve himself.I've honestly seen better stuff from Reigns than Balor if we're comparing the two.
Regardless of all that, the WWE is just taking a chance with the hot new guy. Throw him in a big main event and see how well he does for himself. If Bálor shines, then there's a new main eventer to work with. If not, put the guy back down the card until he's ready again. This whole brand split has been about new beginnings and all, so this is a great way to show it.