The most accurate summary of the passage is:
Cassius says that it is too bad Brutus cannot see his hidden greatness. People are tired and grumbling about the government under Caesar’s rule, and while Caesar doesn’t see the greatness in Brutus, Cassius has heard others wishing that Brutus could be their leader.
This summary captures the essence of Cassius's lament regarding Brutus's inability to recognize his own worthiness and the desire of others for Brutus to take a more prominent role in leadership.