It isn't, the OCS boards are not like promotion boards or any other boards, I know the AF likes their 10 point system but that is how they do it.
The different designators also do different things, the aviation board takes just a minute to look at applications and statements and LOR's don't matter. A board like Supply or IWC will look at everything and can be quite brutal, in the past they have made an across the board cut before the board started (less than 3.0 or anyone who put them #3). The CEC board looks at variety of things but no matter how great a candidate you are if you have a bad interview then you are done, they have also been discarded in the past if they don't have an EIT.
The designators that will scrutinize transcripts are Nuke, CEC, and CWE.
When it is said and done if you have a halfway decent GPA and pretty good ASTB scores aviation is the way to go.