I'm talking about DM skill.Which are you saying is which? Because I'd have called the modern era of RPGs more about clarity and ability to think on your feet while not holding fixed plans.
And I consider both 4e and Apocalypse World to be excellent teachers of how to GM their style.
It's is more important to be clear as a DM in the old school as 90% of the rules are in their head.
Whereas new school tells the DM to know the rules and explain any changes ahead of time.