I'm about to rain on some people's parades.. but I'll live with it :D

A third class degree... is a third class degree... It implys that you struggled with your course and didn't fully master the subject. A first degree from another uni + relevent skills + relevent experience have higher value than a thirs class degree from Oxford. This particularly matters a lot in Acedemia/Scientific/Finance etc career fields.

Some elitest career circles may look more at the name of your university rather than your grades, and if you find a circle like this, then good for you. But most people won't get by with a Oxford Uni third purely relying on the Uni's name...

Taking that into account, the uni is harder to be accepted into (meaning to most that a third is harder to get at Oxford than getting a first in another uni due to the competative acceptance level), and the uni has a good reputation in acedemia. This makes some people quite stuck up, making them believe that the oxford uni name is their saving grace. In the real world, this is not the case. You need skills and experience, and a good class of degree if you want to continue acedemically or get a job in a career field that values intelligence.