Eh, I disagree. I think he can and will improve. Although his structured interviews aren't very good, they're a lot better than they used to be. I mean, I remember watching Conan as a kid back when I was eight-years-old and if I recall, he wasn't that great either. You need to find your footing.
That said, I do think he has some natural quirks that will make it difficult and arduous to fit his style of comedy in the format structure that currently exists. I think he would have better and immediate success by dropping the standard monologue, focusing on the bits and continuing with his interviews where the guests actually do something instead of sit on the couch.