I agree with your points he is a fricken Angel (maybe not pure angel but part Angel either way and raised with the beliefs of the Angels)! Also there is a severe lack of men around these girls so what do you expect to happen when a single male angel is dropped into a girls only school! Of course the girls are going to swarm him not only is he a male he has the perfect body of an Angel! He is the Alpha of all males!
So why do people feel it was too fast? It only made perfect since you put a hot jock into a girls school they will all be fawning over him within a week.
So it's already believable now include that he is an part Angel he is going to exude some aura of authority and we all know girls all love that aura of someone with authority.
So how can anyone feel that it was unbelievable?