I totally agree with you about Jessica. Although she's flopping now anyways regardless if she's pop or country, I think Jessica makes a better country singer than pop. Her voice always had a hint of country, and I think it's better suited for the genre. Jessica as a pop singer never really worked out. She was always outshine by Britney, Christina, ect, and her material was weak and she just didn't seem confortable.
Now as country she is getting outshine by Kellie, Carrie, and Taylor but at least it seems "real". Plus her country album was actually very good. Her best album todate imo. Songs like Remember that sound honest, and are actually really great.
I sorta disagree with you about Miley though. I think if she would have started off as country she could have been successful. Her voice sounds alot more country, than it does pop. Even with her pop songs like 7 Things, she sounds country. Her new song "The Climb" is getting country play and was made into a country remix and I think it's better as a country version. She also had a top 10 country hit with her dad. I think she would be better suited as a country artist, but I doubt she will be successful as a country artist.