At what point do mods step in when a debate is getting derailed?

Not really.

I don’t want to inadvertently snipe, or draw discussion back to the issues of the previous thread.

But it seems to me that a key issue of the previous thread was the definition of "persecution,’ and it seems to me that the issue remains in this incarnation of it.

If someone wishes to link to a Christian claiming persecution, and point out that the claim is in error… is it relevant to point out that the claimant may be using a definition different from one in which the suffering experienced by the victim is sufficiently severe?

It seems so to me.

One cannot, in other words, impose a thread-specific definition for the word and then excoriate a writer who never saw the thread for using the word in a way contrary to the thread-specific definition…can one?