I will admit, DO has the most lore actually relevant to them in game. Zavala talks about their fleets by Saturn, showing that they're out there scouting. The other 2 factions don't get any real mentions.

Well of course.... once you find the dead ghosts, download the app (or bungie.net), find the grimoir cards and read them.... then read them again cause "wtf did i just read? That doesn't even make sense!?" :P