So what might be the criteria for direct appointment versus an LOA?
There are many threads discussing LOAs across SAF.
The LOA is a tool used in various ways by SA Admissions Departments. There is no published criteria.
In general, there is something in the candidate’s record - and it may not be scholastic achievement - that moves the SA to essentially say, “hey, if you meet conditions X and Y (could be a nom and medical), we will probably offer you an appointment.” The language differs slightly across all LOAs.
If a candidate receives one, great, but they aren’t all that common. Many applicants are offered appointments with no LOA, as the more usual path. There are cases where someone with an LOA is not offered an appointment, but that is uncommon.