Diplomacy isn't really an EXP sink. Half of the costs of upgrading it to a certain level are attribute costs, and those piggyback off of Deception. Getting Diplomacy 16 and Deception 24 only costs 26% more than just Deception 24 on its own.
We don't want to spec heavily into Diplomacy, but putting points into it is the mechanical representation of Hazou spending time and effort on it. Half of the 600 EXP we sunk into Deception was spent on attributes, and we can piggyback off that earlier spending to get Diplomacy 16, double what we currently have, for only 100 EXP. At this point the alternatives to that as far as Hazou's specialties go are 1.5 points in Sealing or Taijutsu or 1 point in Deception. Outside of his specialties, Hazou has a number of supplementary skills like TacMove, Awareness, and Stealth that we also put some EXP into. For the same price as 8 more dice in Diplomacy we could gain 5 in TacMove, 4 in Awareness, or 7 in Stealth. I could see it being higher priority to get higher Stealth, and it's absolutely a higher priority to get Roki to 12, but our social failures have caused us a lot of problems, and leveling Diplomacy such that we spend 5% of our total EXP on it isn't actually a large investment.
Hazou now has increased agency to stop the Hivemind from making stupid mistakes but that increased agency only works inasmuch as Hazou is skilled enough to notice those mistakes, and by and large he isn't socially skilled enough to do so. We have to actually try to solve this, and the way we do that isn't just repeating things that didn't work before. We've tried getting "training" from our teammates without any EXP investment, and it didn't actually help. The way to achieve actual success is not to just do more of the same thing that hasn't worked before. Meanwhile Keiko, who had the same problem as Hazou, has paired training and EXP investment and has largely grown out of it. Hazou isn't going to get more socially skilled if we don't actually invest EXP in making him so, the same we he wouldn't get better at punching things if we had him get lessons in it but didn't actually invest any EXP in Taijutsu.
The immediate utility of marginal EXP investment is higher in Roki than in Diplomacy, and in my estimate also higher in Stealth. But Hazou's lack of social grace has been a significant problem, and we have it in our power to ameliorate it. I think that, after getting Roki to 12 and Stealth to effective 15 or so we should put some EXP into Diplomacy.
We have enough EXP to get Roki 12, Stealth 12eff15, and Diplomacy 12 right now. I think we should do so.