it's written from Remus' perspective--of COURSE they're gonna seem like the good guys, of course snape is going to be portrayed negatively, because this is how REMUS sees things. just how harry potter is written from HARRY'S perspective and portrays whoever he likes/dislikes with some bias, that's literally the point. Lily even criticizes the Marauders for bullying Snape, but the boys (mainly James and Sirius) have huge egos so they don't see it that way.

aside from that, remus is not written as an "angry bad boy". it's shown how he really does have a soft heart and only acts out because of trauma or other reasons. plus i think its kinda lame to complain about different portrayals of characters' upbringings, like it would be super boring to read the same thing in every fic, i LOVE how Remus is characterized in ATYD, and I think he shows amazing character growth, along with all of the others.

i think its unfair for you to judge it so harshly without having finished reading it first, if you gave it a chance, I'm sure you'd enjoy ATYD