This isn’t addressing the fundamental question: what makes a practice count as religion? I recognize that Buddhism in different times and places is different. So maybe instead of asking whether Buddhism is a religion one should ask about the character of different Buddhist practices over time. The question though is what would count towards or against any of these practices being characterized as religion.

As for the derailment issue…Because lots of people regard religion in general, and their religion in particular as a good thing they’re inclined, out of charity, to redefine religion in such a way that all decent people will count as religious. E.g. ‘Real Christianity is just following the Golden Rule'. And because of the assumption that religion is important, that it addresses some deep, universal human need, people come up with unintelligible, highfalutin, useless definitions, like ‘the state of being grasped by an ultimate concern’ (Tillich). Since metaphysics is inconsequential and ceremony is trivial they resist the obvious understanding of religion as institutionally organized metaphysics + ritual.

As for a watertight definition of religion, what’s wrong with my three conditions? Do you have any counterexamples? More over, these conditions not only capture what paradigmatic religions are, it also explains why some practices are borderline cases.