Of course, there’s always of what to do with those Dark Lords afterward. The person running ‘Trading Up’ is simply kicking the can down the road. On the other hand, that’s usually a good strategy! A lot of those regimes will just regress to a boring old monarchy or something within one, two generations.
And, on the gripping hand: if there is a problem, there’s also a lot of Dark Lords out there that now owe Trading Up some pretty significant favors…
The world is a big place. IF necessary, turn one dark lord against the other and pray that’s enough distraction for either of them.