You are both right and wrong
For an accurate depiction its effectively useless, but it is useful for overall gauging what people think - this wasn’t a poll dictating anything being added to the game, it literally just gauges player’s interest
Its kinda like the Wikipedia effect; its an unreliable source that isn’t an accurate source, but for laymen use and in 99.99% of cases you can count on it to be correct enough where it is useable
Of course a forum poll like this is slightly differently but when I looked up some estimates of how many people play WoW at this point and I used these numbers to get some rough calculations, the numbers people are reporting of things like “How many get KSM” these numbers seem to fit VERY closely to those figures
So… not a reliable source, but correct enough to matter
Regarding what you mentioned about M+ though you are right, and folks are always going to argue that - seen that happen enough on these forums so thank you for providing a good reference point to refer to here in this thread
But I wanted to focus on the part about a “M+ lockout” and, I don’t think that’s a good idea simply because its unnecessary; as far as I can tell, the average is that folks do 4 M+ a week rather than the full 8, and you only ever hunt after specific pieces if you are min-maxxing and at that point you are making an unnecessary change for a portion of players to which this would matter but only negatively affect everyone
Its one of those elements of design where “Sure we can add it and it would be a benefit but… a benefit to who?”; as it largely would just punish high-end min-maxxers and provide, effectively, no benefit and very rarely a downside to non-min-maxxers