I don't know about Harvard but Oxbridge is definitely demonstrably better. The courses are more advanced than other unis and where else do you get 1:2 tutorials with world class professors? They basically always come in the top 3 in UK university rankings.

https://en.wikipedia.org/wiki/Rankings_of_universities_in_th...

The networking is not a consideration for the majority of undergrads (aspiring politicians are the obvious exception). Prestige is definitely a factor. But that prestige isn't undeserved.