An adequate OS is one that runs the programs you like, either by invoking commands or double-clicking icons. Well, that criterion is filled by the first personal computer.
Graphical OSes. What is the real difference between any modern OS and Workbench? Many apps at one time, not letting a rogue app hang the computer, people still coding stuff for it, and drivers for new hardware.
Mac OS is pretty good at the first while Windows' ability scales with RAM. For the second, most modern OSes are decent at it, while AmigaOS will crash pretty easily if the app is not well coded. As for the third, with Mac OS you get what paid coders make, while for Windows and Linux there's a zillion apps to try and uninstall.
For AmigaOS, not much new development is happening. As for the fourth, it's a hard stretch for anyone to port drivers for AmigaOS, not quite as hard for Linux and Mac OS. The only ones to rely on there are companies still making money off Amiga.
VM is a copout in place of decent memory handling by the app itself. An XP PC with 3GB RAM will do fine without it. Excluded are activities like rendering and video editing. Turn it off.