I believe disassociating oneself is "playing by their rules". Who else has that word? It gives them some closure on you. But maybe YOU need some closure, too. If so, have at it!
This.
Each person's circumstance is different, so what works for me won't work for the next person. I won't DA because I don't accept their authority or position. So F em...
But, for some people, it may be the better option to get the distance they need from harassing elders, family, etc. In that case, I would keep it short and sweet. No point in going thru all the sins of the WTS, they aren't going to read it. Once they see it's a DA letter, and see the signature, it gets filed away, and your name announced at the next service meeting.