It has been the procedure of this SE to not delete questions but to leave them exist but on hold as to not have repetitive questions. Please consider undeleting this useful but on hold question:
It has been the procedure of this SE to not delete questions but to leave them exist but on hold as to not have repetitive questions.
No it has not been, nor is it.
Questions being put on hold (for any reason other than duplicate) is the start of the pathway to deletion. We don't do it right away because we want to give people an oportunity to edit them and get them opened again. Deleted questions are hard to edit, but once it becomes apparent that a question isn't getting edited to be re-opened then the next step is deletion.
In a few very rare cases we've post-noticed question with a lock on all voting and commenting activity, but this is usually when a lot of duplicates have been closed with a reference to it or other cleanup needs to happen before the question is deleted.
Questions that are clearly out of scope for this site that get closed and no effort is made to fix them eventually get deleted.
For better or worse, one of the main ways this site gets traffic is through old, off-topic questions appearing in search engine results. This is great because more people are exposed to the site. At the same time, it's bad because these questions can give the wrong impression about what kind of site this is.
This particular question, Was Catholicism the first denomination?, is very much "primarily opinion based" and therefore off-topic here, as different traditions view this differently. But Affable Geek's answer, summarizing centuries of church history in a few paragraphs, has probably been helpful to many.
Despite the value of Affable Geek's answer, I'm not convinced that it automatically warrants keeping the question around. Remember, the associated cost is that everyone who views that question and answer can easily get the wrong idea about the type of questions that can be asked here.
On bigger sites, the issue of which old questions get deleted is handled by 10k+ users, but this site has very few 10k users who are active with their delete and undelete votes. That means the deletion/undeletion decisions with these types of questions almost always fall to moderators, and it's always easier to question the judgment of one person rather than several.
So to me, especially in light of the general absence of 10k delete/undelete votes, this is a matter of the moderator's discretion. Deleting the question helps prevent new users from getting the wrong idea about the site. Not deleting the question allows the valuable content to remain visible. A third option, applying a historical lock to the question, could also be used, as it retains the content while emphasizing to readers that the question should not be emulated.
One takeaway might be that 10k users should be more active in voting to delete and undelete. But as far this particular question goes, to me the "right thing to do" isn't obvious or clear cut, so relying on the moderator's discretion is the best approach.