Shien is just deflecting blaster bolts back at your enemy. Don't know why Jugs and Guardians use Shien as a dps form when it's called "saber ward" in the game.
If you read The Book of Sith, Palpatine explains how he used xenophobia to keep his Empire powerful by giving the people something to take their anger out on (aliens).
Palpatine wasn't in his prime, as well as Dooku. It's the dark side that corrupts the body, not the light side. The Light side probably allowed Yoda to live even longer.