Among Jimmy Carter's foul-ups is his inability to maintain the unity and loyalty of congressional Democrats. Reagan would face a somewhat similar problem in that he lacked majorities altogether. That said, after a first year of difficulty he would likely be forced to compromise more on domestic policy. That said, circumstance would still doom him.
I could question Carter's inability to deal with Congress but I agree that Reagan would have a difficul time but what about Foreign Policy?
Ronald Reagan probably would have handled foreign policy somewhat better than Jimmy Carter, especially regarding the Iran Hostage Crisis, the Soviet invasion of Afghanistan and the Sandinista takeover of Nicaragua. On domestic policy, I am not entirely sure how Reagan would have done if elected in 1976. He might have appointed Paul Volker as Federal Reserve Chairman in 1977 or 1978 and attempted to pass a tax cut proposal, but that would all depend on how the 1978 midterm elections played out.