I disagree with your assertion of it being something that doesn't exist.
I would assume your basis for that assumption is:
a) You cannot perceive it.
b) You have not seen sufficient evidence/research to change your mind on it.
Neither of those are actually very strong pieces of evidence to disprove it's existence.
The more accurate and truthful statement would be: based on my present level of understanding, I do not think the PRM exists, rather than stating definitively it is false, does not exist and anyone who thinks otherwise is intellectually compromised.
I also think there is a lot of evidence to suggest it is very likely to exist, from which many people have been sufficiently convinced to stake a large amount of their life on, but if you are coming from the arbitrary frame "it cannot exist" it makes it impossible to even be able to consider those points. This is a mentality patients hate, I have seen research showing highly correlates to malpractice lawsuits and is just not necessary.
I think a lot of people don't have the ability to do cranial, but it's good for students to be exposed to it since the ones who can will often go on to incorporate it into their practice and many of the DOs I know who have made the largest positive impression of Osteopathy in the lay public were cranial osteopaths.
So once again, if cranial doesn't work for you, that's fine, but for the reasons mentioned above, you should not attack the practice or anyone that likes it.
To make this all go full circle: I knew a woman who suffered from severe crippling migraines and over a 15 year course was hospitalized at least 30 times and pumped full of narcotics to cope with them, and explored every single thing she could think of that might help them. I eventually met her, had her see a cranial osteopath, the D.O. looked at her, said her PRM was messed up in a few places, explained to both of us on a skull what was out of place (and let me palpate it), corrected the bones preventing the PRM from moving properly, and then my friend stopped having migraines. You can sit in an ivory tower and dismiss things like this, but especially given the weight on the side individuals thinking their is something to the phenomena, and with the strength of your evidence I think it is a much better attitude to be open to the possibility it exists, although if you had to guess it did not.
Anyways there is nothing additional I can say on this subject so I will get back to studying pharmacology and I thank you for taking the time to read and consider what I said even if you don't agree with it!