Drag 'n drop has been in MS Windows and different flavour of Linux distros for the last 10-15 years at least regardless whether the application windows have been maximised or not. Or are you referring to something completely different?
Are we pretending that Windows users don't use cut, copy, and paste instead of drag and drop for file management?
File management in the classic Mac UI was always to open a window for the source directory and another window for the destination directory and use drag and drop to move or copy the files.
File management in Windows was to navigate to the source directory, cut or copy the files, navigate to the destination directory and paste.
Just as the classic Mac OS only maximizes a window enough to show all the contents of the window, but no larger than that to facilitate interacting between multiple windows instead of having every window take up the whole screen.
