I passed my Advanced Police Motor Patrol Officers Driving Course as a class 1 driver in 1978.
I was taught never to cross my hands and don't do so now.
It's not just hand position now that I see wrong on a daily basis these days, lack of lane discipline, failing to signal, driving like a snail on the open road etc etc etc.
It seems driving instructors teach you the absolute basics to get you through your test and the rest is left up to the individual.
My favourite hate is the lack of forward vision especially on dual carriageways, how many times do you see drivers fail to see the slow moving tractor ahead and end up being trapped behind it as they haven't pulled out sooner, I could go on but think you might get my drift.