There's only one thing that neither Steve nor Billy (nor Johnny T. for that matter) have been able to recapture from Jim's Ernie, and that's the laugh. Steve has come close enough for jazz I would say, but neither Billy nor Johnny T. have been able to do it well.
But yes, I've said it before, and I'll say it again, Eric as Oscar has been the single most seamless change I have ever heard, and is the closest I've ever heard a newer performer sound like their predesessor. I've gotten used to him as Frank's characters over the years, as well as David's Cookie; I appreciate what Matt has done with Jerry's characters; and Steve's Ernie and Kermit have been around pretty much all my life, yet you can still detect the difference in their performances in comparison with their predessesors. With Eric on the other hand, there's pretty much no comparison, because his Oscar sounds exactly like Caroll's, which I think is amazing, because I figured Oscar's voice would be so distinct that it would be a challenge to try to replicate.