Yep lawdog6153! That sounds like pretty far-fetched BS, to me! These dealers are sometimes NOT knowledgeable nor reasonable but I would bet it is more that it was your particular "Service Writer", who was incompetent. I would do what "SyndicateZ" suggested and if they start repeating this learning BS, I would ask to speak directly to the "Service Manager". I have found this to work effectively in the recent past with my local Ford dealership in CA.
I had a serious drive-line vibration, drumming sound on my brand new 2023 380-mile Transit 350 Cargo Van. The first Service Writer was not interested in my documentation, TSB or video plus, he was rude and dismissive. I asked to speak w/ the Service Manager but he was off on that Monday so, I came back the following day (Tuesday) w/ an Appointment (made the day before) and spoke w/ another, different Service Writer, this time. He was totally nice, interested in my documentation, TSB & video. They took my van in, fixed it perfectly and I got it back the 3rd day/morning. My point here is that, I am thinking that many Service Writers are not knowledgeable or have had a bad day with a prior rude/angry customer(s). You may have got the brunt of his anger, on that day.
I was worried about the knowledge of the Ford Mechanics (themselves) but after speaking to the Heavy Line Mechanic at my local dealership, before he worked on my Transit van, that he was Super Knowledgeable, if not totally from training, because of him doing hundreds of these things, week after week. (EXPERIENCE!) So, that's my 2 cents worth here. I am hoping you can get your trans fixed soon because it sounds like it could be dangerous, in the wrong situation! I definitely 'would' stay on this warranty pursuit because as time goes on, it's more likely to get denied or put on the-back-burner forever. Best of luck or put that "6153# LawDog" on them, Lance