If one had a job as a aircraft engineer say maintaining the Airbus A380, and is tasked to fix the aircraft's flight system but Airbus does not provide the control schematics for the avionics, then I think all would agree we are in DS. I suppose you could tinker around and try to fix the flight system but in doing so you would certainly be putting your own job and the life of passengers at huge risk. In Indian culture there is the famous story about the blind men and an elephant.
So continuing the analogy, if it is true that PTC are charging 9K for example code so that one can take advantage of the SDK then I assume the outcome could be similar. Especially since very few will purchase the programming manual thus if final calculations are used in the product development area - maybe to produce aeroplane parts for example then one can only imagine the potential consequence. So if PTC Mathcad shortsightedness continues then who knows what consequences lay in store. The only rational option is for existing users to look for another "aeroplane" provider. One may argue that the user is not always correct but if the aeroplane cannot fly and there is no way to fix it then both user and their customers have a big problem.
Ultimately, in our case it is not the user, their customers but PTC that will have the big problem. So in my view, complaining about the Mathcad Prime shortcomings in many ways is altruistic as it has the potential to wake PTC employees from their slumber so that they can engineer a product that they can be proud of and which provides value for money and so ensures PTC long term success. Continuing the flight metaphor, at one point in time we had a peregrine falcon but now we have a Prime Dodo - lets hope Mathcad does not end up as curiosity in some technology museum.