RFPs often lack basic information about the problem the system will solve. They also hate it because they can not answer questions about the problem. Despite management brainstorms and market research they can not tell a simple story of a real person with a real problem that is solved by the website. I have to disappoint them. Usability is not something you add to the design after you're done with the strategic thinking about functionalities.
Usability IS about choosing useful functionalities.
If a website is not useful, making it easy to use or attractive is not going to make it more usable. Usable means useful AND easy to use AND appreciated by users. Even if you choose useful functionalities by change or intuition, you need to know the users and their current practices to know how to design these functionalities in a way that will be understood and appreciated. There is a real risk for designing a user experience that does not answer real user needs and that it is not adapted to user practices. By really listening to users.