We saw four trainees go and make a real difference to people's lives and genuinely be heroes despite being wrapped up in something far, far bigger than any of the other, fully trained huntsmen at the beginning of the last season.

The reason it's portrayed like that is because it is like that. Yes, it's dangerous; that's the point, but nobody believes otherwise. And pointing to what happened to Haven is silly, because that's not the norm at all. Ozpin was dead during that time, the entire world was in chaos (which makes the Grimm much stronger), and Leo was intentionally orchestrating the deaths of huntsmen and huntresses while feeding information to Salem, who controlled the Grimm.

It's nothing like the survey corps. Yes, in AoT, you are almost guaranteed to die horribly if you join the front lines. In RWBY, up until this latest reignition of the war with Salem, it doesn't appear it was actually all that dangerous, or that the 'marketing' was particularly dishonest.