It's there because it tells us a lot about Palpatine and the Empire.So... Yeah, on review... Is this part of Palpatine's plans? Who knows! The Separatists designed the Death Star, Palpatine stole the plans under the cover of a Jedi raid and built it himself after betraying and murdering his erstwhile allies. There's no other direct evidence for anything else.
Jango knows Dooku is playing both sides. Using him as the assassin means using someone he already relies on and not introducing a new person. Jango certainly didn't intend to be followed. If Obi-Wan doesn't go to Kamino, or doesn't survive the trip through the asteroid field, then the plan can still continue, and the war begins with the Separatists launching a surprise attack and Palpatine saving the day with a convenient clone army that a Jedi had the foresight to procure.That's exactly the problem; why not keep Jango either away from the Kaminoans or away from Dooku? Why use your clone-template as an assassin? If these aren't intentional risks to lead the Jedi into a trap on Geonosis, they're bumbling mistakes that only don't blow up the entire plot because the protagonists lose interest For Some Reason. If they are intentional risks, they make sense, but only inside of a plan that requires an implausible series of coincidences entirely outside Palpatine's control.
Dooku, on the other hand, has ambitions of his own that don't align exactly with Palpatine's. He's looking for a chance to betray Palpatine, and a relatively freethinking Jedi can help him with that. So if one of them manages to find him through Jango, they're a potential ally. He's taking a page from his master's playbook and setting up a win-win situation.
The only link between the clone army and the Separatists is Jango, and investigating Jango means talking to the man who hired him, Tyranus. With Jango's death, their last lead went cold, and the only thing the Jedi can do to dig deeper into the conspiracy is to find Tyranus. Dooku left himself the option to reveal that he is Tyranus if he found a Jedi he could work with, but he never did.
The only thing that tipped anybody off that the Separatists were gathering at all was that they attempted to have Padme assassinated because Nute Gunray hates her guts. And Dooku has total control over the timing of the attempts on her life. Although he's been working with Nute Gunray the whole time, he waited ten years before sending Jango after Padme. Why? Because the army is ready now, and it's only a matter of time before the war goes public, so it's acceptable to start risking exposure.
It's also weird that the Death Star plans were complete enough to be worth stealing before the Clone Wars but incomplete enough to allow Galen Erso to insert an intentional catastrophic design flaw years into the Empire (Whatever, it would take a long time to build a moon-sized space station)
The Death Star undergoing design changes and political meddling and becoming a protracted money pit of an engineering project is the most realistic thing about it by far.Nah, the initial plans always have teething issues especially if it's something that's never been made before. They don't magically work first go, and I imagine that goes double for planet destroying super lasers