AmigaOS was vastly better as an OS than DOS. But as a game host, DOS was actually superior, assuming you could get get over the driver issues and the dodgy memory management. DOS was basically a way of loading programs which then had total control over the hardware. Notice, for example, that the PC never really had lots of games that booted directly from floppies the way Amiga games do. That's because DOS games could "take over" the whole system much more easily than programs started from AmigaOS could.
Still, with the advent of WHDload, even that small benefit of DOS is gone