I teach EPQ and lead it in my school. It's not just about the final grade, although the stories of reduced grades are heartening and I know of many in my own school. It's about the skills students learn, which sets them up for university study. We learn about researching, source analysis, referencing, reading academic papers, time-management, effective planning, setting SMART targets, presenting etc. All those come in useful for university study.
Both my DDs did an EPQ, one wrote a dissertation, the other made an artefact. Both were related to their chosen university courses. One went to Cambridge and was asked about her EPQ at interview. She had to do a literature review as part of her 3rd year work, and because she had done the EPQ and knew how to read, reference and cite academic papers, she found it one step up.
However, I know lots of people will say it isn't important; time would be better spent on A levels, which may or may not be the case. What I do know is that on results day, a number of our students who missed university offers by a grade or two have been accepted on the strength of their EPQ grade.