Lots of questions! Let's see.
Chaomancer: corrected. Those first 3 improvements weren't correct at all. Redownload!
nweismuller: a -2 counts as a -3, for basically the same reason that a second +2 counts as a +3.
Borogove on vehicle threats: yes, the vehicle itself is a threat. I hope that looking at vehicles' impulses and threat moves will clarify the reason why. The thing about all threats is that, when they're on the PCs' side, they're still threats to the PCs' enemies.
korik1: it is necessary, yes. It contextually balances risk and reward.
Tim on threats: right on.
Borogove on peacemaker: if it's a trap, you can't justify making the move.
drmigit2: first off, it's not important to me that the waterbearer ever leaves the source. Having a waterbearer in the mix means that you have a strong central location where the characters are likely to be, and that's fine.
Now, it's possible for the hardholder to rob the waterbearer of all power, if that's what the hardholder commits to doing, yes, but it's not a sure thing. Far, far from it. The waterbearer has the single best trump card currently in the game, which is d-harm(water). To take the waterbearer out, the hardholder must accomplish it decisively before the waterbearer can take the move embargo. Otherwise the waterbearer can hold the entire hardhold hostage, for real.
And in general, it's never a question for me of how the playbook's going to defend itself against the others. They aren't designed to that purpose. It's a question of how the playbook's going to be useful to the others as a friend and ally. My suggestion is that the hardholder is far better off not getting into an escalatory war with the waterbearer, but instead making the waterbearer part of their approach to dealing with the rest of the world.
Still: the waterbearer starts play in a tenuous position, and it's in their interest to solidify it by making allies and gathering reinforcements. That's very true.
Ell975 on lawbringer: it's an intentional choice, yeah. It's all about the waterbearer's initially tenuous position.
On the child-thing and more generally: along with the faceless, these playbooks aren't going into the core set, so they're an opportunity for us to play around a little more with how the game works and what the things in it mean. You should consider them to be variations on Apocalypse World, not simple expansions of it, if that makes sense.
-Vincent