Haha yes, they didn’t care much about smooth controls back then. But once you’ve gotten used to it, Ultima Underworld is actually very playable. Although I’m using a dpad (mapped to WSAD), I also have an extra “Walk” button (mapped to s) on the right side of the screen. This way, I can walk with the right thumb, and steer left/right with the left thumb. That’s much more convenient and precise. I only use dpad up (w) when I really need to run, e.g. when I want to take a long jump.
It might even be a good idea to have walk and run on the right, and only turn left/rifgh and strafe left/right on the left side of the screen.