As an almost exclusive PvE player, I legitimately have been surprised by the amount of people that feel this way. I personally never coveted the faction armor, since it pretty much is the same as the vanguard and so I never exchanged mats for marks, especially since spending 30 to 45 minutes to get the 50 you needed was not at all worth it. I have found the new material exchange to be a god send though, since I tend to get around 200 marks a week for my 3 characters while just doing dailies, weekly 28's, nightfalls and public events. I was literally drowning in marks with absolutely nothing to use them for beside randomly buying a piece of armor to break down for ascendant shards once every other week. A couple of weeks ago I calculated that I needed around 4.5k materials to fully upgrade everything I have. I do agree though that there is no reason why you shouldn't be able to buy faction gear with vanguard marks if you feel like it.