The ba'ku planet is, legally, a federation planet, subject to federation laws - a state claimed by the federation and recognised by the major (read - relevant) powers in the region.
No, it isn't. To be a Federation planet, it would have to have applied for membership, been vetted in detail by the Federation Council, and been approved by a majority of the member worlds. The Bak'u colonists had not done so. Their world had been independently settled, meaning it is a sovereign territory — one to which the Federation has no legal claim.
Actually, it is Federation territory, according to
canon.
Admiral Dougherty said so specifically in 'Insurrection' and Picard did not contradict him (meaning it was most definitely true).
There are numerous worlds that fall within the "territory" nominally controlled by the Federation that nonetheless retain their autonomy: Nausicaa, Orion, Capella, Organia, and Ventax, to name a few. By your reasoning, each would be subject to seizure by the Federation under eminent domain, but that's clearly not the case. In the Original Series, we saw many independent colonies reject Starfleet interference or inclusion in the Federation.
In many episodes of Star Trek, the Federation has been shown to be respectful of sovereignty of populated worlds, whether their populations are indigenous or colonists.
These worlds were, obviously, recognised as independent states/colonies by the Federation (at least).
Unlike the ba'ku planet/people, which did not have this legal status.
Also - Nausicaa, Orion, etc in Federation space? Where is this established?
Or are you basing this only on these species appearing in Ent/TOS, implying short travel times to reach them (travel times which, as we know, are unreliable, Qo'nos being 4 days away from Earth at warp 4.5 in Ent)?
You yourself called Nausicaa a neighbor of the Federation in 'Destiny: Lost Souls', yes?
What Admiral Dougherty tried to do in Insurrection was akin to a U.S. military commander trying to seize the Caribbean island of Grenada simply because it was found to be a source of rejuvenating fruits. You can argue all you want about "the greater good," but the action taken remains illegal.
In order to exercise eminent domain, the real estate to be claimed must demonstrably be under the direct authority of the state. Mere proximity is insufficient legal basis.
As I already said, the ba'ku planet's status as federation territory is canon.
Its exercise also typically requires the service of legal process to the property owner and the right to contest the action in a legal forum. There is no evidence that any of these steps were even attempted or considered in Insurrection — again, making the entire undertaking illegal.
True. Admiral Dougherty&co acted idiotically/illegally on more than one count.
None of this changing the fact that the Federation had the legal right to expropriate the planet.