yes and no but it based on what card and what setup it for, usually it non metas
Not anymore for almost all of them.
They really need to update the drops....
It's sort of an illusion progress to make up for what you're really farming for which is the super rare gem drops. Mostly are the shadow of their former glory, nerfed to support incoming new deck.
You still need to grind for duelist skill drop though if you want to use a certain skill.
most of the cards you can get from legendary duelists are trash. there are some exceptions like the blue eyes, but you can get those pretty easily with in-game card coupons or via unlocking their respective duelists (like unlocking kaiba or mokuba unlocks 2 blue eyes)