ALL exotics should have at least some chance of being obtained from engram drops. You shouldn't be required to play pvp for an exotic if you don't enjoy pvp, and most of these pve exotic quest are just ridiculously sadistic... it's not even remotely fun or enjoyable being mercilessly paddled repeatedly for hours upon hours trying to get a reward cookie that's most likely just going to end up collecting dust in your vault... RNG has always been more exciting anyway...