If you think the difference of custom and high end universal IEM is not that big to justify the extra cost to spend in order to get marginal benefit, that would be the same case for some middle level IEM(PFE& Qjay) and high end IEM.
Like UM3X is not going to persuade everyone that it is equivalent to threefold quality as PFE. I think each step up to next level is most likely 20-30% gain for performance. As long as urge for audiophile to pursue high quality persists, manufacturers can easily exploit this to get as much as profit they can get from us