I think probably app-defined palettes and a global menu is best possible combo.

The app-defined palette enables more rich functionality as you’ve mentioned, while the system-owned global menu provides a consistent way to see everything an app is capable of without hunting and pecking through the palette. The menu also serves as a unified API for assistive and automation technology to interact with software and allows users to choose how the menus are displayed (don’t like a top-aligned menubar? Cool, your desktop can present it as window attached menus, a pie menu, or NeXT style floating menus or anything else you can imagine).