I take in all your points, Bj?rn, but common sense still tells me that the six who do all the work and have chosen the candidates will steer the rest of them in the direction they want, as they, and their experts, will have examined all the information much more thoroughly than the rest of the 18 (some of whom are too old to take an active part in any decision-making).
I wouldn't imagine that the other Academy members do very much more than rubber-stamp decisions made by The Six, plus a little input on recent works by candidates, which may sway the 18 one way or the other. The method described on the Academy's own page does undoubtedly look very fair, and obviously, the members have built up a knowledge of what certain recurring candidates have written before, so they would only have to read their new works.
The basic point I am making is that it looks to me as if the six people listed have much more say than the rest. For reasons of efficiency, this may be legitimate, since they are literary people of long standing. It looks like what happens in a national parliament: an executive committee does most of the work, while the full parliament has a vote, but is firmly guided by the committee.