I'm not so sure, it could be argued both ways for both sides, but I do think it's better as it is. Way I see it, Mercenary Armies mean handing out this whole 'for Motherland!' business to foreigners, Assimilated Peoples is kind of 'they're basically us, they just don't know it yet', seeing how assimilation works in HK (I still think there should be another possibility of turning them into mini-vassal, that would prevent them from going extinct, but they'd keep their city, just provide you with resources, and portion of money and science).

Can confirm this is how it was since release.

To me is seems OK

- use money to field mercenary armies (world)

- cheaper independent city assimilation (homeland)

Also, in the early game Homeland is greatly preferred due to the +1/+2 combat bonus versus the measly 5/10% food bonus.

So pairing cheaper mercenaries and more combat bonus seems a bit too strong.