It depends on the context. If the loss of control of character is a known possibility of play, and the player is aware of this and makes decisions accordingly, then it’s a negative consequence of play.
Has the player lost full control of the character? Yes. Does this mean the player has no agency? I don’t think so.
Perhaps in your opinion it’s boring. Others may find it interesting. Either way, we do learn something. In the example
@pemerton gave, we learned that his character wasn’t as ruthless as he’d believed.
That form of revelation may not be to your liking… that’s fine. I don’t disagree with your preference, just your description of it as not learning something.