All too often, the GM is the one who has to say no.
If you look at it realistically, martial arts were generally better than the unarmed combat traditions in the west in the modern era. . .now the military teaches variations of eastern tradition martial arts. . . .if something works, other people will take it for themselves.
If Knights find themselves being taken apart by Samurai moving at double speed, history says they will take one of two routes. . .label the Samurai witches and burn them all, or learn to do it themselves.
So it's hard to avoid the logic that if the Monk like character is thrown into a western Europe like scenario, that people may start to copy them . . .if they can. In RM, it's just DP, so if one person ever convinces a monk to train them. . .the genie is out of the bottle and these esoteric skills are being taught in fencing schools across the continent.
Which means that a really useful skill can really only be rare for a brief window of time. Martial Arts were essentially unknown in the west the 1930s, and part of pop culture by the 60's. (Admittedly, life moves a lot faster in the information age, but even 100-200 years is really the blink of an eye in history.)
So unless the skills are REALLY expensive for non monks, they'll become commonplace. . .much like various eastern or eastern inspired martial arts are common in the west now. . or the fact we almost all use Arabic Numbers.
Which makes it hard, for me at least, to control skill based adrenals, short of railroading the PCs. . . .like the moment the Monk PC starts training the other PCs in adrenals despite my warnings at chargen, a posse of Elder monks shows up to stop them. (And if the PCs want to fight them. . .I tend to consider a TPK to be a loss, not a win). . .it almost gets to the point where I either just consider them rare, but not restricted skills, or just completely cut them out of my games completely.
On the other hand. . .I never seem to have such problems with the Monk semi profession base lists.