That's me out then!
Havin gone through school, uni, professional qualification and now ATPL ground school; I'd put them, difficulty wise, alongside A-levels. However, there may be a "kudos" level which may be higher than that on the basis that fewer people are in a position to study ATPLs. Someone either has to get accepted on a cadetship or sponsorship, pass interviews and selection criteria or they reach a position in life where they can be self-funded - not something that an A-level student needs to go through.
Of course, I am talking about 1980s A level (proper ones!)
Cheers
Whirls