1. As I said, each map gives you around 3 levels worth of XP of on-demand content. That's 3 levels worth of XP in a 10 or 15 level map. Doubling the XP would push that to some 6 or 7 levels. That's 7 levels in a map that spans 10 or 15 levels. Add the PS, add events, gathering, ... and players could easily get the needed XP.
Heck, this would could lead to folks not needing to explore the full map before moving on: which, as mentioned, is something I am a massive fan of because it leaves content on maps that players can return to.
2. Downscaling. If players gain too much XP, the game downscales said players making sure that the content is still challenging.
Doubling the XP gains for the whole game is as close to being the best solution for this mess that I can see: the game is made more approachable while A.Net isn't forced to waste hours upon hours on fixing things.
Just double the XP for everything.