They were presented about as comically evil as the Falmuth leaders though, the only difference being that they're implied to be in some form of servitude, possibly as part of the summoning ritual like Shizu was. The Touma-looking dude and the girl were particularly bad. The quiet guy not as much.
Contrast them to Shizu or the kids, and well, they came off as two-dimensional evil just like the rest. Maybe they'll give them some backstory.
The scummy shit is that Falmuth is going to send those three, have them "rampage" and then use any resistance or attacks on those three from Tempest to claim "their citizens" were attacked and invade.
The logic that "Because who would believe a bunch of monsters?" is really shitty though. Rimuru already knows the leaders of other nations, and depending on your POV, most demon lords are monsters.