While I understand what assumption you're running under no one said for only billionaires to pay. The idea is progressive tax brackets the less you make the less you pay percentage wise. We also need less loopholes for the people that can buy lawyers and manipulate their funds to get out of paying what they should. There is no reason companies and the extremely wealthy should be paying an effectively less tax percentage than the diminishing lower middle class.
It's not about only billionaires paying, it's about them not being a magical money source. A higher rate might feel better, but it's not solving government revenue problems.
It will not suddenly balance the budget but it is funding that will either reduce the deficit, or reduce the burden on poorer people. We can't fix decades of poor decisions with one good decision, it's simply a good decision we can make now that will help.