The Destiny 2 dev team posted about some changes coming to XP earning on the Bungie blog.
XP was scaled while playing longer activities or fixed duration ones like Crucible competitve multiplayer matches. XP used to scale down in public events. Bungie commented that they are not happy with the results and have heard the same from the community. The full post is available here. The changes are as follows:
As a result, players will see XP earn rates change for all activities across the board, but with all values being displayed consistently in the user interface. Over the course of the next week, we will be watching and reviewing XP game data to ensure that these changes meet our expectations, as well as yours.
They will also be posting updates on this system through their official channels.
Source: God is Geek