Pretty In Pink

One thing I think people overlook when they say "the Jedi should have listened to Dooku on Geonosis" is that Dooku had already betrayed the Jedi Order. Regardless of whether or not you think his disillusionment with the Jedi Order was valid, he quite literally betrayed all of them in the worst way possible.

Dooku could have just walked away, but instead he decided to weaponize the compassion of the people who had trusted him for years, and he fell to the dark side. Dooku became cruel, unmoved by the plight of others, used his own powers to oppress, and killed without mercy.

What reason did the Jedi have to even trust Dooku on Geonosis? Why would the Jedi suddenly take Dooku at his word after he had already demonstrated that he was willing to deceive, manipulate, and kill? "Well Dooku was right and the Jedi were too arrogant to believe him" when he fully betrayed their trust. Obi-Wan rejected what Dooku was offering because he refused the dark side, but he still reported everything that Dooku said to him back to the Jedi Council afterwards.

The Jedi address this at the end of Attack of the Clones. They make it a point to keep a closer eye on the Senate, which becomes increasingly difficult for them to do because the war is keeping them occupied. It's almost like Dooku telling Obi-Wan about Darth Sidious but not telling him that Darth Sidious was Supreme Chancellor Palpatine was all part of the whole game. He revealed just enough to make the Jedi suspicious, but that still wasn't much to go on. Even if they had suspected Palpatine was the Sith Lord, they had no proof.

It's not an accident this was revealed to them just as the Clone Wars began. It wasn't like the Jedi were standing around doing nothing while Darth Sidious gained more and more power. They were dying in a war they actively tried to avoid. A war that was orchestrated by two Sith Lords whose ultimate goal was the destruction of the Jedi Order and, eventually, unlimited power.

it'll be like old times again