The devel/ncurses port provides many libraries:
> $ pkg info -l ncurses | grep lib/ | grep "so$"
At least libpanelw.so and libtinfo.so are missing in /lib, and maybe more libraries are missing.
Please note that the header /usr/include/panel.h corresponding to libpanelw.so is present.
The ncurses port is at version 6.2, and the base ncurses is at version 5.x.
Take a look at /usr/src/lib/ncurses/ncurses/Makefile and you'll see that libtinfo is a symlink and a number of other libs are all symlinks. Everything is built into one lib and symlinked, which isn't ideal but is how it's historically been done. Base ncurses probably needs a bit of an overhaul.