It doesn't necessarily make kids more compliant for the convenience of their parents. Methylphenidate is the most common first course of treatment which takes around 8 hours to completely leave the system. This means that most children will come home from school with no enduring effect. If anything, it can make some children more difficult and more manic in the evenings after a day having been on it. In the three weeks of my son on this, there have been three evenings where this has been the case (I got a surprisingly powerful punch in the gonads one evening!). The other 12 evenings he has been absolutely the same as before he tried meds (i.e. a pretty well behaved kid but noisy like kids of his age are!)
A zombie effect, or a making a person into a robot come from a dosage that's far too high, which means due diligence hasn't been followed during titration. They aren't an expected side effect, they are indicative of a dosing error. What the drugs actually should do is raise dopamine and norepinephrine to combat anxiety and impulsive behaviour, i.e. making a person able to be their real self and focus.
I think downers have been prescribed to people who haven't benefited from uppers, but they aren't the first line of medication, they are a last resort. Perhaps they might zombify someone, but it's unlikely anyone would be prescribed these without having tried a variety of stimulants at different doses.
My experience so far involves having to track every change to my son's behaviour on a daily basis and if there are significant negative effects that's exactly what titration is for, to adjust or change medicinal treatment.
Sad to hear that some people seem to have experienced a process whereby that due diligence hasn't been followed.
If I experienced anything like this with my son, or any hint that meds were suppressing his personality then I'd pull the plug pronto!