We've seen drones act mindlessly many times. Even Hugh, who ultimately did show individuality, started as a mindless drone. However, Locutus was able to speak with more agency, and Seven was nearly a complete individual when she was first introduced. Seven in particular, during the events of Scorpion, had nuances and emotional dialogue.
What was different about these two Borg?
Locutus was specifically "made" to facilitate assimilation of mankind as an "ambassador". Seven was assimilated as a young child which probably had special implications as well, in addition to becoming yet another facilitator in Scorpion - I don't think her backstory ever clarifies whether that caused the Collective to "upgrade" her characteristics for similar reasons, or whether she was more human all the time.
