I do find it "easier" on lower levels, in the sense that builds are simplified & streamlined. And it maximizes wonder production never building settlers. But that is only viable as long as you can out-tech the AI with only one city.
So when you get up to higher levels, OCC becomes pretty tough. You don't even get to use food trade routes to help your city grow. Diplo victory may be within reach with the right policies, or domination with certain civs, but culture and science wins are both challenging. You can't generate as many great scientists in OCC, and your base GPT is capped at a low rate so science victory would be very, very slow. Science also affects culture profoundly...you will probably get beaten to the crucial Renaissance wonders by the AI, and it's tough to recover from that.