Don't take me too literally about the word "religious" - it was shorthand for describing an approach that isn't based on empirical evidence, such as an a priori that "one size fits all". Most professional print makers I have read or discussed the matter with, and based on my own experience as well, will advise that's it's best practice to examine the choice of RI one photo at a time. This makes sense both empirically and theoretically. Empirical is each person's taste, so there's no point spending much time discussing this except to say that print appearance can vary depending on the photo and the chosen RI, and different people will prefer different renditions. So be it. But the theoretical considerations are worth bearing in mind when deciding whether to be "religious" about it. After reading the descriptions (Real World Color Management, 2nd edition pages 88 and 89 by Fraser, Murphy and Bunting) of how the RI treats the photos differently, especially relevant to out of gamut colours, it should become immediately obvious why the recommended best practice remains best practice.
As for how well softproofing works, depending on the quality of the profiles, the display, the soft proof settings and the experience of the user, it can be a very reliable indicator of what to expect from the printer - not perfect, but god enough to reply on - that's the whole point of it.
