I have seen comments from people who had vac schemes that there was no clear pattern amongst their group in vac schemes. They probably have a method, but I don't think it is as easy as 'this competency/WG percentage gets you in'. U are right in that 65th isn't looking great though. Honestly, hope for the best and prepare for the worst.
Not that I think you should read much into it, but I applied last year and got rejected for the summer vac scheme. My top competencies were excellence and leadership preference, and the worst one was respect. I was in the 60th percentile in the WG. This year after having done a vac scheme and TC offer somewhere else, I am applying Direct TC, and my top competencies were motivation and critical thinking, my worst was commercial thinking, and my WG percentile was 77th.