I don't know what kind of work you do but let's say your work requires you to log into some kind a system that somehow knows to track the work you do. Now imagine you start your work and your co-worker logs themselves in your place. You do the labor, they get the benefit. Are you being cheated?

The VA would do that labor if there was no TTS with their voice as a model. The VA labor goes into that model because it is their voice. They do the labor but someone else benefits from it? Are they not being cheated?

And final thought experiment. If the VA-s owned the TTS system and Embark asks for a new voiceline. Are the VA-s supposed to give that new voiceline away for free just because some TTS system generated it? Wouldn't Embark cheat them out their pay if they said "You made it for free so we should be able to use it for free."?

The intellectual bankruptcy comes from you because instead of actually thinking about the situation you hide behind the "But they agreed to it" argument. People also agreed with indenture servitude, doesn't mean it's acceptable.