This is perfect- you've created a very firm defense. I'd like to add that Snape, knowing his cover was going to be blown, had the option of taking out Granger and Ginny Weasley- a Mudblood and blood traitor- as well as one of Dumbledore's staunch allies, Flitwick. Instead he merely knocked Flitwick out and pretty much ignored Granger and Weasley.
The only person he attacked was Dumbledore.