opportunistic manipulation of the young man's distress and vulnerability
Dumbledore's M.O., apparently. How strange that the author's interpretation (and some critic's, as you pointed out), is that Severus' appeal to Dumbledore was a weakness. I agree with you that it took strength and courage to face his greatest bully with an appeal for saving Lily's life.
That Severus did not alter his course against the wave after wave of personal disappointment and abuse by those in whom he placed his trust is a great testament to his courage. How easily it would have been to NOT protect Harry, especially as the boy never acknowledged Severus' efforts. How terrible that Severus had to witness harry's fawning adoration of Dumbledore, when Severus was truly one of the few people protecting Harry at all costs.
I need to stop, or I shall weep for Severus the boy, Severus the teen, Severus the man.
Excellent points and conclusion.