I'm going to caveat this news with a pinch of salt, and say that there's no confirmation of this from Bioware, but it seems that there's the potential for freeplay, and the open world "dungeons" of Anthem to drop far more Legendary and Masterwork items in comparison to Stronghold. It's suspected that due to the spawn waves in Strongholds, compared to out in the game world, there may be restrictions on drops. Having tested this yesterday, running solo dungeons in Freeplay, I have to say there feels like there's something in it. Half an hour of play yesterday saw me grab 4 Masterwork's and a Legendary. I've never had that happen, despite repeatedly running Strongholds. I can't promise this'll work for you, and it's best done in pairs, but heading out to the archways on the map should see you quickly encounter enemies to beat. Here's a snip from the original source, Moosee999.

There's a scorpion dungeon that I've gotten 5 legendaries from, but for all the scorpion world events - never got a legendary. I've done sooooooo many scar world events and never got a legendary from a scar during the event, but random scars just chilling have given me 6 legendaries. Never gotten a legendary from a dominion during a world event, but have gotten 9 from dominions just hanging out after work at their little camps. I've killed probably about 3x as many faction during world events vs out in the open, but never had one drop anything during world events. I've started to just kill in sheer numbers of enemies that are NOT part of world events and my legendaries per hour goes up and up and up.