It doesn't necessarily matter how much freedom they had or didn't have. It could also vary majorly from person to person (though this arc didn't make it look like that), but Ace clearly held Whitebeard as the next man down from God himself. Even the stabbing guy betrayed Whitebeard for jealousy, not because he wanted to replace him (showing "healthy" ambition, if you can call it that). They were all living for Whitebeard's glory. I don't believe Whitebeard actually wanted this, but he was so big he couldn't help it.

What happens next is another question. Unlike Ace, some of the other captains actually might be able to naturally go and live on for a future of their own.