Agree with what you’re saying but there are many hair transplant doctors that do not use finasteride or promote finasteride and are very educated on the (very serious) risks. It is definitely not something that is required or needed as part of a hair transplant – if the transplant is done by a competent surgeon. Fin will potentially help prevent future loss if that is your pattern, but it should have no bearing on the actual transplant, again if done by a competent and good surgeon. There are a ton of guys who get a transplant due to either failure of finasteride or severe side effects from it, or they just don’t want to be on a medication with a published history of causing permanent issues in some men - a lot more than Merck originally disclaimed in their clinical trials and post trial followups.
As you said, the scariest part is his arrogance and telling folks there is nothing to be worried about. That’s extremely poor medicine.