I have been acquainted with Tippy for nearly ten years now and can confirm that he has no bias, at least not in this area
Although I personally tend towards verbosity in my writing, I can confirm that any English professor will tell you that conciseness is a virtue, particularly when correspondence is unsolicited. Quick and to the point is best in that it grabs and holds the reader's attention.
You can certainly do as you like, but I would agree that your letter is likely to get more mileage outside the message board if you stick to the facts dealing with how you were personally affected/harmed/wronged by the experience. Speculation is more likely to weaken than strengthen your argument, particularly if that speculation proves false. For example, while you speculate that Grant's method for holding the lottery may have been part of King's contract with Grant, I think it is even more plausible to speculate that King's refusal to exert the effort required to sign more than 800 copies of TWTTKH despite there being 1,250 copies of LSOE is evidence that he did not particularly give a damn about the 450 individuals who would be left without a copy and probably could care less how Grant decided to allocate any unclaimed copies.
Either way, what is the end game here? King has been working with Grant for over 30 years now with 13 (off the top of my head) signed/limited editions. In the absence of stealing from their customers, refusing to issue refunds, or some other major offense committed on a massive scale, it is unrealistic to believe that King is going to even consider severing his relationship with Grant. Were you to have been unhappy with your copy of the book and were Grant to have refused to issue a complete refund, I imagine that you might have been able to get King's office to intercede on your behalf (if not your credit card company). It sounds like Robert has been apologetic, and I'm sure that if you are so disgusted with this process that you want a refund, you have it (unfortunately, King's comments about his disdain for collectors lead me to imagine he would have very little sympathy for the money you shelled out on the secondary market for the LSOE, so you're almost certainly out of luck in that regard). If the goal is just to let King's office know that you had a bad experience, make that be the point of the letter rather than trying to use it to rail against speculated transgressions or to convince King not to deal with Grant in the future, which are messages that are much more likely to fall on deaf ears.
Let me close by stating that I am certainly not biased towards Grant, as I have had my own odyssey dealing with a damaged signed/limited and can therefore understand your anger and frustration (at least in your case your waiting did not result from their sending your book to a wrong address over 500 miles away despite your repeated warnings to the contrary). I'll also apologize if the length of this made Tippy or anyone else out there nod off