The jedi don't, or rather didn't, exist to police everything. They simply aren't going to go to worlds where slaving is common and likely lawful and force their views on those places. The essentially said in the prequels that their numbers were low and they could only do so much..
In as far as Rose and Finn go, the options were, free the kids to, the what? streets? to fend for themselves? They barely got off the planet on their own and if they did, they're taking to a ship being beat down by the FO where they stood a substantial chance at dying.
The broom kid was to show the effect of luke's sacrifice and that there were others out there who were going to follow in his footsteps. That doesn't mean I like what they did with Luke at all, i don't, but, that's what the point was I just don't think they made it clear enough. Shoulda made it more like play-acting 'i'm Luke Skywalker!' as he pulls the broom to himself.
As for the books not being page turners, meh, semantics. Stories are page turners. Instruction manuals generally are not. Doesn't mean in the slightest that there isn't valuable information there.
All that said, my point in asking the question above was that there's nothing they have to do in the next one. If there was no IX, there's nothing to say along the lines of 'but what about...' As noted, it's pretty wrapped up right now. I was excited about what happened to Luke post ROTJ, too. They never did anything with that. And it wasn't needed in the context of 4-6. What does Rey do next? That is NOT a compelling story for the capper of a trilogy that was supposed to cap 1-9 as well. The only capping thing that i can think of is Leia's funeral. We're capping 1-9 by killing off any lingering aspects of 1-6 and doing so in a generally all around crappy way. But I digress
There isn't anything they HAVE to do in IX. That's extremely problematic for a trilogy. There's supposed to be an over arching story that completes in the third act. There's nothing left open for the third act.