I think the problem is that you're more likely to get worse gear or even gear for other classes with the engrams. Trading wouldn't be better given how you didn't exactly "earn it," but at the same time, PVP does the complete opposite and is completely wacky. If the legendary and exotics you get from engrams are only for your class, so you wouldn't get a Hunter helmet for your Titan, and if the Cryptarch wasn't such a jerk, this wouldn't be a problem.