I think that's an unfair and gross generalisation. Firstly, Oxbridge does not like applicants to have studied law at A level, as it's considered a soft option for A level.
All the law applicants I met when I applied this year seemed to know a great deal about their subject and had done work experience over the summer.
Don't assume that everyone else applying will be any less qualified than you are. Everyone who applies to Oxbridge knows how hard it is to get in and will have worked very hard for their interview.
Bear in mind that Oxbridge has a very low dropout rate, so it's unlikely that there are many applicants who have 'no passion for the subject'.