You want the person managing the speed to be focused on that if managing speed is still inherently and unavoidably attention-intensive - if modern control technology is able to automagically maintain speed at x knots, adjusting all the various engine control parameters to implement that, then an extra person in the loop only means an extra chance for mistakes or delays.

If the military learned a lesson from exploding a reactor with an automatic control system, you might never know - it's not required to be reported to the public.

If an automatic control system can blow up a reactor so can the manual one. You have a problematic design issue in both cases. You can also still assign someone to keep an eye on the reactor in case things go bad an have that person pull an emergency stop or warn the guy in charge. There is no reason to relay every little speed change through several people.