The kill-death-maim-loot XP loop is why a lot of folks moved to milestone-based, but there has been a lot of backlash to that in recent years and I guess it is because the rewards feel more disconnected from the player actions, or even biased towards railroading ("no level up for you because you turned LEFT when I wanted you to turn RIGHT")

Giving XP for anything that you want to reward is the way to go I think, and keeping it transparent so the players know what will be rewarded. That said, if they know their mission and they achieve that, it is very similar to milestones anyway.