There’s nothing wrong with splitting up the characters, but copying that formula three more times is Lazy. So, in ESB it’s fine because it’s done the first time.
Except that is probably the single most common thing to do in a story. It isn’t just Star Wars, it just just about everything out there. Any time you have a group of characters, you get through more story, have more interesting dialog, and just about everything else is more interesting when you split the company up. Some characters get into more trouble that way. It is probably the single most common story structure I am aware of.