A few things, even though I agree that people went wild with the theories, the blame is ultimately Marvel for even setting up so much double worded meanings, Easter Eggs and mystery as to what's going on that lead to people coming up with these theories. Especially the biggest blemish of the whole Quicksilver. They purposely put it out there for people to theorize and go ham with it then played along with these fake leaks and sources and actors acting all smudge and coy about "special guest stars" and in the end NONE OF IT MATTERED. People still are acting like this show was "setting up" Dr. Strange or Spider-Man and really it's not. There's no point to say it is based off the point they wasted these so-called hints as bullshyt. They could of just told a STRAIGHT UP character arc story about how Wanda's grief and depression led up to her becoming the Scarlet Witch without all the nonsense and Easter Eggs and so-called clues that maybe or maybe not be part of other MCU installments. And you wouldn't have these wild theories. But Marvel baited it and it bit them in the ass. That's why the director of the finale had to temper down expectations because they realize they created something that gotten overblown.
2nd, the finale is BAD regardless. And I believe people would of been upset no matter what. It's no so much about being wrong, but dissatisfied at what they did show. A good contrasting comparison is the finale of the Mandalorian season 2. There were wild theories and predictions leading up to that finale, but EVERYONE was satisfied with what they got which both properly concluded that seasons why successfully setting up things in the future along with spinoffs.
Lastly, the biggest problem: The resolution with Wanda. All that occurred and nothing from her to learn from it? What was the whole point of this series? Granted I know it's an origin tale of Scarlet Witch with a subplot origin of Photon.Spectrum, but it felt unearned. As if Marvel wanted to tease that Wanda's a villain, but they rather use half-measures rather than make it clear cut which is why the finale is befuddling. Even Monica's character arc is weak and unearned as to her connection with Wanda, because we don't see an example shown to Monica grieving or feeling a sense of loss. No emotional connection. Or no emotional connection between Wanda and Agatha. Agatha would of been the most interesting character, but the finale had her resorted to another cookie cutter villain, when technically she wasn't truly villainous at all. Nor Director Hayward. I would of respected it more had Marvel WENT THERE and made it clear, cut and dry that Wanda is undoubtedly the villain, Monica the HERO, Agatha more of an Antihero, and Director Hayward a by the book agent. Then had Monica be the one conflicted as to convincing Wanda to do the right thing, still defying Hayward, but so make the decision of trying to stop or fight Wanda once she realize that Wanda is too far gone. This showing the contrast of how Monica could overcome her own loss by witnessing how far gone Wanda has gone. Even with Monica unable to stop Wanda because of her being too powerful, at least it would give reason for her and SWORD to seek for someone like a Dr. Strange. But that's just my opinion.