Meg - actually, as someone who has been a freelance editor/proforeader for years, it is a relatively easy career for someone to rock up in, say, 'yup, I'm a proofreader' because they can spot typos
, and they may want to become an instant member of SfEP.
The current membership structure is the best way of 'upholding editoial excellence' and imposing some sort of standard on an industry in which it is easy to claim competence where you have none. If you have been proofing for years you only have to get 6 points - iirc - of training, which is not that expensive - and is also tax-deductible.
As I said to issimma above, if you feel you have a case to become a member/advanced by another route than having all the points in the way the SfEP wants, then you can contact them and explain that, and they will look at individual cases to judge each on their merits.