After complaining last week about the size and scope of the Realms, and their hodgepodge, jigsaw puzzle world design it dawned on me that Conan's Hyboria had a very similar world design and it didn't matter there at all. Look back over the Conan stories and they'd open with him in pseudo-Egypt, or running from native tribsemen, or dealing with no-quite-vikings or what have you. The lack of highly realistic integration in Hyboria didn't matter. So why does it feel like it matters in the Realms?
I suspect there are a few reasons:
First, the more narrative the players are the more they want to detail every part of their PCs lives. You need permission in advance to just say "OK, in the last 6 months your adventuring company has made it from Waterdeep to Arm, and have taken command of a merchant ship heading south...." even thought that makes them appear more broadly competent and powerful in that these things can be glossed over.
Second, mechanically the game now favors rapid PC improvement. In earlier editions your PCs took a long time to move through the key levels of 5-9, and therefore could have several different stories at the same relative power level. That's certainly not the case in 5E, especially since levels 1-4 are your 'origin story'. I tried to run a Conan style game with Captain Fasaad where the crew of the Daud would arrive somewhere, have a adventure and move on, but each adventure had at least 13 encounters of her CR, so every adventure Fasaad would level up and, by the nature of D&D, become better at fighting. That perpetual escalation lends itself to a sort of narrative, where as Conan started damn tough and got a little tougher but a lot more broadly skilled. (At least with my players Fasaad also got more broadly skilled since the players never tight focused their skill points).
Third, the breadth of the Realms in any one area sell themselves to small location until you're on sweeping quests and then return home sort of play. It has a lot of politics and trade baked into it.
Fourth, Conan often starts adventures broke, and D&D places a lot of PC power in their gear, Players would freak if you kept taking it all away. This, at least, is something 5E should work against.
I think I'd be much more comfortable with the Realms in a Conan style, where I move from adventure spot to adventure spot with little bridging stories. I'll have to give it some thought.