Correct. It is easier to prove guilt under Article 86: Absence Without Leave because the proof of intent to remain away permanently required under Article 85: Desertion, is not required. Simply a cut-and-dried matter of absence from their unit without permission.
For absences exceeding 30 days, the maximum punishment under Article 86 includes either a BCD or DD. This is enough since getting rid of the defendant in a punitive way is really all the service is looking to do anyway. In addition, the AWOL deprives the defendant (and especially the defendant’s activist lawyers) of the opportunity to turn the proceedings into a political show. Since the issue is absence and only absence, any discussion about WHY the defendant went AWOL is immaterial to the charge(s).
Sort of a win-win situation for the service: get rid of the dirt bag AND frustrate the activists.
From what I saw, the Navy for the most part automatically declared UA (unauthorized absentee) personnel deserters at 30 days. I think this was mostly for the purpose of freezing pay especially now that everyone gets paid by direct deposit. Also in conjunction with your point the declaration of desertion could made immediately if there was evidence the sailor never intended to return, i.e. a note that says "I'm never coming back".
A guy from my division on my first ship deserted. He cleaned out his locker of everything except for a cigar and an ace of spades. WTF? Nobody knew what to make of that one.