Owain Glyndwr,
system gain (roll acceleration/stick movement) was reduced as the airspeed fell, but against that you have to set worsening dutch roll damping and increased roll/sideslip ratio as AOA increases. And I don't think one can exclude Bonin learning how to fly it!
The slide slip and the yaw rates were not oscillatory before 2:12:15, the spiral mode is predominant. After that yes, at large AOA, the natural Dutch roll damping is slow, it requires a lot of effort and remarkable skills, to preserve stability...like standing on a ball, while holding a large umbrella in gusty wind. As far as I know, all the crashes due to control lost (stall) ended up in a spiral dive. Bonin kept the wing leveled, 38000ft stalled descent, i.e. see between 2:11:30 to 2:12:15, he used left rudder and sideslip, to increase the lift on right side of the wing, since roll command was insufficient, at left stop