FDA trials are only required to compete against a placebo. A drug is accepted if it is safe and more effective than a placebo in a double-blind clinical trial. That's it.
So they have no data to show with, unless they went above and beyond to get it. (Which should teach them a lesson about testing their drugs.)
You don't have to have head-to-head data to claim your drug is superior to existing therapies. Yes, head-to-head data is the best way to show it, but if you have two separate trials, each comparing to a placebo, you can draw conclusions about relative efficacy. It's not perfect, but in the case of Gilead, their drug blows away anything else currently on the market.
