The prequels are a study in subtle story telling. It is never made truly clear what Palpatine is doing. But if you watch the PT enough you can see that he is playing both sides and he has many avenues to get what he wants. He lays the plans for the demise of the Jedi around the time of TPM. He plans to corrupt Anakin and make him his apprentice. The only real hint is when Jango says he was recruited by a man named Tyranus. The question is if Syfo Dias was really the Jedi who ordered the clones of if it was Count Dooku playing the part.
There is a lot that is not explicitly stated and we are left to guess.
Lucas shared his thoughts with Dave Filoni and he shared them in the behind the scenes of the Mandalorian. Those make sense.
Qui-gon was the Master Anakin needed. As the three Jedi duel on Naboo, Anakin’s fate is being decided.
The Jedi don’t see that they are failing Anakin. They tell Anakin to just not have feelings. He has feelings and they never teach him how to deal with them to avoid the dark side. Their whole attitude toward the dark side is to just avoid it. The whole fear leads to anger leads to hate leads to suffering starts with just avoiding those feelings. Anakin is a mass of feelings and needs to deal with them and the Jedi have no idea. Qui-gon would have taught him how to deal with his feelings. He was the only true Jedi in the PT and with his death the course to Empire and the fall of the Anakin and the Jedi was sealed.
So I think the corruption of the Jedi is very much PT canon and has nothing to do with Clone Wars. I could see it before Filoni started Clone Wars.
And I did not read the novelizations or most of the EU. So what I saw had to be just what is in the three PT movies.