That’s just about the opposite of the relative experience of the actors involved in both trilogies.
The original trilogy was filled with almost completely inexperienced actors. The prequels were mostly cast with experienced performers, excepting the child actors of course.
The real difference is that Lucas didn’t actually direct most of the original trilogy in the first place.
I mean, George Lucas hired Harrison Ford as a carpenter because he wasn’t interested in doing a second movie after American Graffiti.
Mark Hamill was probably the most experienced member of the original cast because he had done some TV work.
Natalie Portman had starred in four features before Star Wars and McGregor had done more than ten.