Dutch Roll does seem to vary from nothing to something you simply can't practically compensate for manually. I heard of something smallish (Kingair maybe) that you couldn't control even if you were really psyched up for it. The 747 by contrast is servicable with no working yaw dampers.
I don't think you could even taxi a Trident safely without the yaw dampers operational.
(I admit, I stand to be corrected on all of this)