gnome-panel doesn't need gnome-shell. The dep was added as a band aid for upgrade from F-14 -> F-15. Its says so in the spec:
# Band aid for "yum upgrade"
ARM devices and the OLPC XOs don't have the ability to run gnome-shell due to the lack of accelerated drivers with 3D and they tend to have very little space. For F-16 or 17 it would be nice to remove this artificial dependency.
Fixed in 3.2.0-2