The research in the link is interesting; what would be particularly instructive would be an EPQ/non-EPQ comparison at equivalent A level grade outcomes ie what do degree continuation and outcome data look like for, say, AAB with EPQ and AAB without?
That would be more revealing of potential EPQ value added as it helps strip out wider effects which are likely to see more academic students, at better performing schools, being more likely to be encouraged to take EPQs (but who might do well at uni anyway without an EPQ).
It would also be interesting to see research on the numbers of students giving up their EPQ prior to completion and the drivers for that. It sounds like @Malbecfan's school takes care in how EPQs are promoted; at my DCs' school they were definitely 'over sold' and drop out was high.
EPQs appear to take up a lot of time; this can be worth it for the right student but the skills can also be developed via NEAs as part of A levels (eg Eng Lit, History, Geog, CompSci), albeit within narrower subject-specific constraints. This releases time for other areas where useful skills for uni and beyond can be developed eg paid work, volunteering, sport etc. As ever, the position is nuanced.