Other than the leaked financials, I haven't seen any leaked or public information specific to the US alone that suggests that one is subsidizing more than the other. They could be subsidizing equally. Or Uber could be subsidizing more. Or Lyft could be subsidizing more.
Do you have any evidence to demonstrate that only in the US Uber is subsidizing more? If so, please share. I haven't yet heard a single convincing argument supporting this popularly held belief that Uber is subsidizing more.
All I know is that all of Uber's business is more efficient than Lyft. Plus, this is after taking into account that Uber shoulders most of the market's losses when it comes to penetrating a new market and getting laws changed to allow TNCs. Once TNCs are an established business in most markets, the legal costs should drop, shrinking G&A, thus leaving it even more capital efficient.