There's a huge difference between legitimately disputing an ambiguous term and dismissing an argument wholesale by demanding a detailed definition of a generally-understood term.
Okay, so this isn't really a point about definitions.
I'm not asking for a comprehensive definition of religion because I somehow don't understand what a religion is. I'm pointing out that there is no trans-historical or trans-cultural category of religion, and thus that the definition of religion which we "generally understand" is actually kind of irrelevant to the context and the people we're talking about, who did not have the same definition of religion (or indeed any definition of religion).
To quote anthropologist Talal Asad, emphasis mine.
"My argument, I must stress, is not just that religious symbols are intimately linked to social life (and so change with it), or that they usually support dominant political power (and occasionally oppose it). It is that different kinds of practice and discourse are intrinsic to the field in which religious representations (like any representation) acquire their identity and their truthfulness. From this it does not follow that the meanings of religious practices and utterances are to be sought in social phenomena, but only that their possibility and their authoritative status are to be explained as products of historically distinctive disciplines and forces.
The anthropological student of particular religions should therefore begin from this point, in a sense unpacking the comprehensive concept which he or she translates as "religion" into heterogeneous elements according to its historical character."
In other words, the anthropological approach to religion (although the same applies to a historical approach) cannot simply assume the "generally understood" definition holds true in the field, because it is only "generally understood" to us as modern people with similar cultural reference points, not to the people we're actually talking about. If our goal as historians or anthropologists is to understand those people, then we can't simply pretend that they lived by or adhered to our category of religion, because they didn't.
You need a "so what" to your arguments here. Present an alternative definition of religion and state why that affects the thesis. Otherwise it's mere nitpicking.
Also, one thing I think I made clear is that I don't actually disagree with the "thesis". I disagree with the way that the category of "religion" is treated as a self-evident feature of a historical society which lacked a concept of religion, but I think in a general sense the thesis works. If we assume (for our own heuristic purposes, or even just for the purposes of fitting a confusing world into easily understood game systems) that participating in Jewish rituals makes someone of the Jewish "religion", then the OP is probably correct that the Jewish diaspora lead to people "converting" to Judaism.
What prompted my response was seeing a legitimate criticism of the method used to arrive at this claim dismissed as "wordplay" because it references, correctly, the fact that the category of "religion" does not exist in the time period under discussion. Apparently though, pointing that out violates some principle of scientific objectivity.. who knew?
A common problem with newer commentators (like 21st century internet denizens) is that, in keeping with the intellectual trends of the time, they often seek to create general rules from particular circumstances, such as creating categories like "older sources" to describe huge swathes of very different writers, sources, and scholars as if they possess an underlying similarity by virtue of not being contemporary.
You are aware, I hope, that a tendency is not a general rule.
