He didn't damage the ticket
I'd say he did, by bringing the association with the GOP House and his widely disparaged budget plan, further painting Romney as out-of-touch and giving Democrats tons of ammo to attack Romney with.
But I read in the Romney Readiness Project that the main reason he was picked was because he and Romney went together like clockwork. Ryan was the numbers and data guy like Romney, and would act like "an adviser reporting to the manager". Their personalities clicked.
Of course, in the end Obama was going to win.