It says something that he's starting to feel like he can believe her on that point - that it is hard to feel like this could all be some ruse to trick him into coming back to them. If it was, he feels like she could have manipulated him much easier but expressing the importance of him taking back the role. He likely would have felt compelled to bend to it, if only she were to push.

But she hasn't. This entire time, she's never even suggested that it's the choice he should make. Considering everything Optimus Prime means to the Autobots, that is more meaningful than anything else she could do.

"But it is what you would want," he says. It's not a question - it's a statement of fact. There's no bitterness in his words, just a plead for truth. "Were I to decide to reclaim the Matrix on my own, it would be what you were most glad for, would it not?"