Exactly. The Combine has to give a little, and the Republic doesn't want a mostly operational world in the Dragon's clutches.
So the Combine agrees to hand over Prosperina and other such worlds in exchange for the chance to purchase the output from other, more damaged, Hegemony-era factory worlds. Also, it would have been a key world that the Davions would surely want to strike, so saves the DCMS some effort in keeping it safe, and serves Stone's agenda of creating peace.