You have two finesse backers who excel when they're told to just attack. Don't think, just attack. But you're asking them to sit back and read and react. One guy has no lateral mobility, so he's already behind the ball on any "react" plays. The other has great instincts, but has absolutely no ability to get off blocks and often runs himself out of plays.
They have to give Jaylon and LVE set responsibility on every single play. One of them should probably be blitzing on every play, the problem is that means the other is probably covering.
I think if it was just Jaylon, or just LVE, they could be schemed into playing well and making lots of splash plays. The issue is whoever is left to read/react IS going to blow it every single time.
I believe LVE and Jaylon can be successful together. I believe they can be formidable together. For that to happen, however, this defense needs a dramatic makeover. I know everyone wants fat guys in the middle, but it's more delicate than that. Dallas needs an intelligent penetrating DT who doesn't guess wrong. They need that DT to make the calls back to the LBs so they know which gap he's hitting, so they know their assignments.
Whats happening in the Dallas defense is a critical failure on every level. Not enough talent. Poor scheming. Poor coaching. Not putting players in position to take advantage of their strengths. Poor skill pairings. The whole defense is trash, top to bottom.
I think it's going to take at least two years to field a strong defense. They have to decide on an identity and scheme and then get the talent for it.