The panel itself is not the problem, it's the lack of integration with windows. In GNOME, when you maximize a window, the title bar stacks underneath the top bar. If that window also happens to have a menubar (e.g. LibreOffice) that gets stack underneath as well.
This is just a lot of wasted space and makes the menubar harder to click, compared to having the menubar at the very top, next to the screen boundary.