Look, you among some others in this thread keep confusing 2 things. Meta =/= Deckbuilding. Just because something isn't popular right now doesn't mean that if a deck isn't build exactly a certain way, it isn't good. I've heard this "but but but, a million people have worked on these perfect decks!" several times as an argument for this, but... no. Concepts for a deck have always been from a few, and extremely few stray from it. Look at the story of the Shieldbearer and Doomguard, that says it all.
Conversely, deck building is more than putting 30 cards together and trying it out for a few games which is what a lot of times the discussion tries to center itself around. Just because a list of 30 cards wins some games does not mean it's ideal. It doesn't even mean that it's an actual good list of cards; you can win games with bad decks and you can lose games with good decks. Figuring out all of that is the bulk of deck building, not just putting a list together; being able to tell when the list itself is why it's winning games and not just outplaying opponents (or when the list is causing problems and not just your misplays, etc.).
Also, I have no idea what posts you're referring to that mistake "meta" and "deckbuilding." Maybe I give posts more credit than you do but I'd like to think most people get that "X is a bad card" refers to now and not forever (unless otherwise indicated, anyway). Card strength is relative to the current meta which in turn dictates archetype options. "Viability" then is more in reference to aiming for the best winrate vs the rest of the field since that's what Ranked grinding boils down to. And then if this isn't for Ranked, a lot of the details matter a lot less.
Then there are tons who think they did brilliant tweaks by swapping 2 cards. Whoop de doo. They did squat for the deckbuilding scene. And guess what decides the meta? The ones who actually make original decks.
Not quite true. The meta is dictated primarily by the day-to-day playing. Which is pretty much the realm of individual tweaks. What shifts the meta massively will be either a new deck or of it the small tweaking here and there exposes something for a different deck to take position. There's been very few "new" decks in the past few months, usually just reiterations of older decks or straight revivals of old decks.
Besides that, "Deck building" has this broad meaning attached to it. Was Freeze Mage coming back just a revival of it? Or was it a new deck? I mean, it was a ~26-28 card mirror of the old deck. Was Malygod Rogue a new deck or just Miracle Rogue with more spell burn? What's the line for the variations of Ramp Druid to be new decks? Zoo is old Board Control Warlock with a lower curve, is that really a new deck or a tweak?
You can say that the meta currently doesn't have a lot of decks with a lot of Legendaries in it besides Control Warrior. But you cannot say only that specific class has use for multiple Legendaries. What makes you think a Cairne or Ragnaros has more synergy in that deck than say a Control Paladin?
But nice backpedaling.
"people don't know how to construct good decks"
-into-
"it's not that other decks loaded with legendaries are necessarily bad it's just that they're probably not optimal"
That tone change.
I feel like this is you just reading into it how you want to. The original post in question is complaining about seeing 5+ Legendaries in every deck. Quite frankly, the most common situation will either be the common Legendary heavy Control lists or just random lists with a lot in them. It's not necessarily about "only Control Warrior would ever do that" but more "If you're facing off against it consistently, it's probably a bunch of Control Warrior because that's the most common deck to do that right now." This doesn't exclude niche decks from the equation but those certainly will not be the majority case.
Besides that, I find it funny you take the "only Warrior would do that" here to literally mean "only Warrior would ever do that" yet want to make the point earlier that card assessment is a fluid thing dependent on the meta, other card choices, or even just bad assessments.
Also, I'm not really sure why you keep feeling the need to use "netdecker" as some kind of derogatory term. Sure, you can have some pride in making your own decks but to pretty much try to constantly insult people in the thread for not making their own decks seems a bit much.