Not that WAR is the be-all and end-all, but in 30 starts, Leake had 1.5 fWAR. On top of that, it was a down year.
On the other hand, Kelly had a career year--which covered 24 games including 16 stats--and ended with only 1.0 fWAR.
Both Leake and Kelly have room to grow, and I wouldn't make any guarantees about either of them having a better future than the other. However, saying Kelly is "far and away more talented than Leake" is borderline asinine imho.