How can you entirely discount marketplace dynamics? If Uber has all of the drivers signed up then the users try switching to Lyft but no drivers are available then they will go right back to Uber. Uber has raised billions and are seemingly making a lot of money so they can easily afford to fight legal battles around the world.
That's the biggest long term problem, uber can't create platform monopoly without hiring drivers or illegal employment practices. They can still thrive, but it will be monopolistic competitive market where they have to rely on branding/reputation and less concrete platform lockin effects.
They pretty much have to allow the drivers to drive for competing networks, or qualify "partner" as an employee. So Uber marketing budget in some ways helps Lyft, Sidecar and Wingz.
