So there is a lot to unpack and maybe I'm not the right guy for the job. But seeing how I exclusively perform material that is classified as "mentalism", I think I might have some insight to offer. That being said, my opinions are subject to change.
Firstly, I think mentalism is a wide net, so what I consider mentalism might be different from what others perceive as mentalism. So my answers are solely based on my experience and my opinions.
Anthony is completely correct, there is no evidence for real psychic phenomena. But the pseudo-methods presented by many mentalist (photographic memory, reading body language, covert hypnosis, etc) aren't scientifically accurate either. So either way, the performer is "pretending". The only difference between the two is that narrative they want to tell. Do they want to tell a story of paranormal powers? Do they want to weave a story of science fiction? As long as the audience is aware of the context of the performance (understanding that it is a theatrical performance) I don't really care what the performer claims.* The end goal should always be to entertain the audience to the best of our abilities.
As far as "real methods", I think they have their place. I use both hypnosis and CMR in my work with great success. But I also see a ton of value in using billets, peek wallets, and impression pads to help elevate mind reading. I should mention that I don't use any memory displays, but I don't see the harm in using real memory displays with a "pretend" method. I am reminded of Ricky Jay and his amazing abilities. He had phenomenal slight of hand, but was still open to using gaff cards.
*This isn't to say that I am okay with people claiming to have real powers and be able to contact the dead. I am firmly anti-conman. That being said, I also think its unethical for a performer with zero experience or formal education in sales to teach at training seminars. Either way, the person is using methods to attempt to pass themselves off as the real thing. I find both dishonest and problematic.