Well I realize this comment is WAY way too late, but screw it, maybe you'll see this somehow.
Ross, I think you're being unfair to Picard here. He did the space equivalent of pulling over to help someone change a tire, only to realize the vehicle was involved in human trafficking. None of the actions of these societies are his responsibility; the de facto enslavement is clearly not ideal from a humanitarian (or whatever term applies to aliens) perspective, but Planet A had GENERATIONS to figure out what Dr Crusher figured out in five minutes, and Planet B had that same time to come clean. Both societies made their bed, it's not Picard's job to lay in it.
Also, while you're clearly thinking farther into the future than the episode intends, I think maybe you're not looking far enough. Interstellar travel in Star Trek is not some arcane technology developed by a special few. The damn Klingons figured it out, and they're basically space vikings. If Planet A survives, they're going back to space within a couple hundred years. And they're going to be PISSED at Planet B. I mean, just think of all the problems American Whites and Blacks have with their troubled history, even living next to each other to separate individuals from stereotypes. When this video released, there were race riots happening. With the situation between these worlds, Planet B's reputation on Planet A would make the Jews' opinion of the Nazis seem like mild disapproval by comparison. When, not if, Planet A got back to space, they'd be gunning for some payback for those guys that lied to and enslaved their ancestors for generations. And as you said, Ross, Planet B would be going agrarian, assuming they didn't all die out. Agrarian societies aren't known for their space programs or weapons research (other than Fritz Haber), so even if Planet B survives the massive shakeup, they're staring down the barrel of brutal enslavement and/or genocide by Planet A within a couple hundred years.
Would love to hear your takes on other ST eps, btw.