Research experience, mostly in terms having RA is everything. And by everything here I mean the quality of your references. Other "experience" is more or less useless in the eyes of the admission staff, especially in the UK. Don't even get me started on the importance of research interests and areas in terms of a broader research proposal.
Do not assume grades are easy to get. Sure, for top places grades and GRE scores are merely the cutoff, but saying that "any higher grades make no difference" is utterly wrong.
You are competing fiercely for funding and everything matters.
The video was overall extremely annoying and irritating. if you are going to promote yourself talking about a career in academia with the seriousness and performance of a "10 things boys hate about you" video, at least provide information that isn't wrong.