Get rid of Starfleet as the bad guys.
Have it so the Sona are there with the permission of Starfleet, who thinks they are conducting scientific research on the magical properties of the rings. Data found out that they are really planning to harness those powers (which will destroy all life on the surface), and that's why he went crazy. The Enterprise goes to get him back after the Sona demand that Starfleet removes him. That way it turns into Starfleet (in the form of the Enterprise) against the Sona, making the central conflict more clear cut. The grey area comes from whether it is right to sacrifice one planet to save billions, not whether the other Starfleet guy is your enemy or not.
Subtract your first sentence and that's pretty much the movie in a nutshell.
I'd much rather it be Starfleet vs. Starfleet than being exposed to yet another rubber faced alien we will never see again.
But in my version, we never have starfleet on the planet working with the Sona. The way it is muddies the waters. Is Starfleet or the Sona the bad guys. If starfleet's the bad guys, why do other starfleet guys act like the good guys. Keep things clear and simple. Sona are bad guys, starfleet good guys.