IMO there's still a misplaced assumption by some employers that if you're an Oxbridge grad you'll be more able than other grads to convert superb academics into whichever skill set is needed for a particular job.
My trade is predominantly populated with people from Oxbridge. Some are unarguably brilliant at the job. But others are recruited straight from the colleges without any evidence of capability in the actual role.
It's not unusual to find oneself working alongside extremely naive and, often sneeringly arrogant, young people of this background.
The latter may have succeeded over competition from other top ten universities with equal honours and often over candidates with tangible evidence in the form of a hard won, post-graduate, portfolio of work.
All of these youngsters were exceptional at the gateway to tertiary education. Oxbridge, however, can encourage a belief that this potential does not need any further development.
Then, later on, the ones that fail miserably are rarely turfed out...
This is usually because of the highly established and effective alumni network, or outright nepotism, due to Oxbridge educated parents/relatives, to whom they may turn to pull strings.