I agree in that the stakes for 3 are incredibly low. It starts trying to save Rocket's life, but that's nowhere near the same level as playing keep away with an Infinity Stone, or stopping a mad god from destroying the universe.
Rocket dies, or he doesn't, it has an impact on a dozen or so characters.
Then, once Rocket's life is saved, it becomes keeping him away from the High Evolutionary, who wants to use Rockets DNA to fuel a new race of beings just as creative (and destructive?) as Rocket.
But this is, ultimately, Rocket's origin story. The flashbacks are heartbreaking, and, yeah, even though it's smaller in scale, it has more emotion behind it than 1 and 2. It's about the characters and each gets a chance to shine (even Cosmo!)