I don't know. If we follow that line of thought one could argue that Argonians aren't sentient at all. They're just an extension of The Hist. In other words; we haven't really been playing as Argonians all along, we've been playing as The Hist.
Only in the sense that you've never been playing as men or mer, you've been playing as Ehlnofey.
The nature of sentience is the core theme of the Elder Scrolls series. Nothing is itself, everything is a sub-gradient of something else. The Argonians are a sub-gradient of the Hist. A clear distinction is made between the Hist and the Ehlnofey, which means that the rules which apply to the Et'Ada -> Ehlnofey -> Men and Mer relationship do not necessarily apply to the Et'Ada -> Hist -> Argonian relationship. It doesn't mean the Argonians are less sentient then men and mer, only that the Hist are more sentient than the Ehlnofey.
Like the Ehlnofey, the Hist spread their selfness out amongst a mortal race, but unlike the Ehlnofey they left behind physical forms as an anchor, the trees themselves. A Hist tree maintains a self-awareness that extends to its Argonian "descendants", something that the Aedra do not have. This anchor allows the Hist to reach out and reassert its own will upon its fragments simply by overriding the self-ness of the Argonian in question. It's clear, however, that the Hist don't normally do this: chances are good it is not without cost, since whatever it was about Mundus that forced them (and the Aedra) to subdivide themselves presumably is still in effect. A mass recall might weaken a Hist or even kill it, or maybe the opposite would happen, it would grow too large (metaphysically) and the other Hist would feel threatened and destroy it lest it consume them all.
It doesn't mean the Argonians don't have a will of their own, no more than the fact that each Man/Mer is made up of fragments of gods does for them. The only difference is that the Hist can reassert themselves upon their fragments while the Aedra cannot. We have reason to believe that Argonians are capable of resisting the recall (and apparently, individual trees can resist the combined will of the Hist hivemind) but we have no idea how difficult this might be, or how common Argonians/Hist capable of this defiance are.