I would say that the ATPL syllabus is at least as complex as my degrees (undergraduate and Masters level). And is both denser in parts, and also more pressured than many university degrees.
And while the comments about modern requirements for other softer skills (CRM) etc are entirely valid, I would say that the assumption that those equivalent skills are imparted during some bog standard first degree at an average university is a false one.
I personally think that it is the extra-curricular side of uni life that can give a student that additional dimension to their education, and for that to happen the student must have to have embraced that side of life.
So people who were super academic to the exclusion of all else won't necessarily have had much of this uplift. And at the other end of the spectrum, neither willl the millions of undergrads who just stumble through their first degrees and divide the non lecture time between study and socialising (ie not volunteering, not joining clubs or societies etc).
And for both of those sets, I personally wouldn't necessarily assume that the skills required as a bedrock for some of these modern cockpit 'soft skills' are going to be in place.
In short I think what I am saying is that in agreement with sentiments earlier in the thread, that to all intents and purposes you may as well say that an ATPL pass is equivalent to a uni first degree - it's a fair bit of work but it's not rocket science, and it doesn't guarantee you have additional skills that may these days be important in a modern MCC environment.
Therefore the O levels I assume are merely being used as the bare minimum academics required to make sure you could for example actually do the maths required in the ATPL theory (trig etc)
Hope that makes sense