The only whose been hairsplitting is you.
You keep changing the dynamics of the argument when your points are picked apart.
Either the Ba'ku planet is or isn't a Federation planet? This is the sole argument that matters. If it is, then the Federation is within its right to relocate six hundred inhabitants under eminent domain. If it isn't, then the S'ona should be free to either work a deal or wipe out the Ba'ku to collect the radiation.
Do both options suck for the Ba'ku? Yep, they sure do.
You haven't picked anything apart. You've started out with your position that the good of the many outweighs the wishes of the few, and you have shaped your arguments around that. You've started with a foregone conclusion and then tried to work your way to justifying it. My approach is more legalistic, in which definitions matter, jurisdiction matters, and the Federation's own supposed values should be taken into account.
It is "a planet within Federation space." It is absolutely not a member of the Federation. That Picard makes this distinction is apparently important. The Federation is not free to do as they please with the planet and its inhabitants, because it is not a "Federation planet." That is an entirely separate
point from whether the Federation should protect the Ba'ku from the Son'a. The Federation may not want known Dominion allies poking around in their backyard, and they may not be keen on watching a massacre happen that they could've easily prevented. The Federation would have no legal
obligation to protect people who aren't Federation members, but it'd still be kinda shitty for them to stand by and watch a massacre happen in their own territory.
What they absolutely should not
have done is get in bed with Son'a and try to surreptitiously move the Ba'ku in order to harvest the metaphasic radiation. Doing this to a group of people without their informed consent--indeed, without even warning
them you are going to do it, and with intent to actively deceive
them when you do it--is simply wrong.