"Forever" was hyperbole, apparently that wasn't obvious. They have existed for a very long, long time, ever since items actually started permitting them to. Support itemization actually becoming a thing was a pretty big deal, you likely remember that, if you're bringing up S2?
There've been other times where the support pool has shrank down to something like Braum/Leona/Alistar as well. It's not unheard of for mage "supports" to not be in the meta.
That was one one poll (started on reddit, if I remember right?), and it's less than 8k votes when there are a massive number more players for League that either play Zyra or decided to vote regardless. tl;dr a single Strawpoll gathering results from primarily one source is far from foolproof analysis. It's also still open for votes meaning the results are continuously fluctuating.
The percentages haven't changed since about a week after that poll was made. When I was analysing it in the thread it had the exact same percentages. There is no fluctuation.
As for the sample, yes that's not every Zyra player obviously. What it is however is a very large set of people. Even the most upvoted comment in the mid year thread was at +200 with just over 300 votes.
The thing about that poll is that it is the best available snapshot of people's opinion on the matter. You say 8k like it's a bad thing, 8k is several times larger than anything else we have.
And, yes, they were barking up the wrong tree. Riot already had a set idea for her rework by the time people chimed in, and it's hard to say how much the opinions shared by players really influenced that.
Riot's idea was wrong. Companies aren't perfect, sometimes their ideas are just bad. Zyra is the 'new Coke' of League. Riot thought she was better, they assured us she was better, she tested well. None of this matters though because in the end all that matters is player perception and she gets an F for that.
Her rework was pretty great, from the revised mechanics it gave her — more frequent plant spawns, the ability for plants to actually have enough health to survive a stiff breeze — but it didn't really enable her much as a solo-laner, which was a definite shortcoming and probably an intentional sacrifice to prevent her from overruning support (which is now apparently a concern, although again I disagree with it). Regardless, "complete and utter" is a massive exaggeration.
Riot's rework of Zyra was abysmal even from a design standpoint. They made her at the mercy of RNG with her dumb passive. Her army of plants is BS to play against and honestly less fun than her old playstyle. They took away the skill required to use Q in any way. They destroyed quite a popular style of play. It was an abysmal and catastrophic failure on all fronts and should be reverted in the same way as Kog's, pre rework Zyra wasn't perfect but she was certainly better than what we have now.