Poor instrument scan is a problem in initial instrument training and in simulator training too, but I cannot understand how that translates to a need to reduce used of FD's. Rather, training that reemphasizes airspeed control, attitude flying in absence of reliable airspeed indication and, indeed, in normal flying is a critical need as well as engine monitoring and so on.
I have no idea how many pilots I have trained for jet transitions and ATP's.
Basic scan has rarely been a major problem in training.
However, doing type ratings for very experienced pilots has sometimes presented scan problems, but seemingly only for pilots who've never faced an actual emergency. Thus, I think good simulator training in emergency procedures with instrumentation failures is highly effective in maintaining proper scans.
Nothing induces good scan techniques so well as partial panel IMC approaches IME.