I'm not 100% sure how flagging works here either, I guess. But it seems that I declined your flag, so I should tell you why.
I think that a flag for "primarily opinion-based" shows up for moderators, with the following options
- close the flagged question instantly
- delete the question instantly, or
- "clear" the flag without further action. (This is called something like "No further action...")
Since the question did attract a popular answer, I didn't think it was fair to instantly close/delete the question, but rather allow for the community to decide on its fate (through the standard 5 close votes), maybe allowing users to suggest improvements, etc.
However, on the user end, the last option of "No further action..." results in the flag being "declined". In some cases, there is an option of deeming the flag as "helpful", but I guess this is only true for comment flags...?
(As far as I can tell, this isn't really documented anywhere and with the few flags that we have here, I still haven't figured out when we can mark a flag as "Helpful" without deleting/closing the question instantly.)
As you observed, the question was closed soon after by @Flaw.
So, apologies for the confusion with your flag. If I had had the option of marking the flag as helpful, I would have done so, but without taking any further action, but it seems this was not possible.