I have maintained from the very beginning that the People interview from 5 of Meghan's friends, apparently done with her permission (otherwise how would those 5 friends have known the details of such an intimate letter?) was an absolutely terrible idea, and this is why. The public didn't need to know about Meghan's contact with her father, and the DM certainly didn't need to be tipped off to the existence of the letter. By portraying him in a negative light, Meghan's father had incentive to turn the letter over to the DM to, in his eyes possibly, set the record straight. It's one of several serious lapses in judgment as has been discussed endlessly on these threads.
I'm not excusing the DM, and I personally hope Meghan prevails in the lawsuit, but there wouldn't have been lawsuit at all if Meghan's friends had been discreet, and if she had not given them the go-ahead to share the details.
I am afraid you are rewriting history. Mr Markle was all over TV, specifically GMB with Piers Morgan, saying he had no contact with her since the wedding, that the phone number he had was disconnected, and that she was ghosting him (incidentally Piers Morgan's talking point). That narrative was being repeated in UK media (print and TV) a lie even internationally even though it was lie. They 5 people who talked to People magazine were rebutting that false narrative and it is in this context that they alluded to the existence of that correspondance.