Should I go for a PhD in Oxford University?
If you will think of time spent on the PhD as time wasted, don't do it.

However, in considering the pros and cons, do remember that PhD students who are having problems are much more visible than the ones who are enjoying the experience. 

Supervision should be a benefit, not a downside. I remember some very interesting conversations with my academic advisor.

People working excessive hours, other than for short periods during emergencies, are less productive than those who are getting enough sleep, exercise, and social life. 

If you experience isolation, you are doing it wrong. A PhD is a time to network with other researchers in your chosen field, including but not limited to fellow graduate students.

Writing your thesis may be the one time in your life in which you can write about your research area without limiting yourself to a few pages. Why would "thesis work" be a negative?