Excellent point about Harry. The Defense Professor virtually certainly knows Harry's opinions on the subject, whether by his mental model of Harry or by observing him telling anyone who'll listen that Hogwarts is dangerous.

On the other hand, I believe we've seen Harry failing to convince Hermione of something she was morally set on, much like this. (Anybody remember the specific incident, or am I imagining things?) Once Hermione had refused Harry's entreaties for her to leave, it would have been much harder for the Defense Professor to change her opinion.

And finally, there's this:

She couldn't have described it in words, what triggered the realization, unless it was the sheer pressure that the Defense Professor was exerting on her.

Which supports your argument that he's being a little too over-the-top. The Defense Professor is above all, subtle - this kind of all-out effort is not like him. Maybe there's some time constraint, though, and he doesn't have time for "subtle?" Aargh.